Introduction

My dissertation comments that "this collection is far from exhaustive: it is based on an examination of a minute fraction of the relevant musical literature." The same statement applies to this supplement.

Byrd (1994) discusses a handful of these counterexamples. A related collection of examples of unusual music notation is my Extremes of Conventional Music Notation webpage. That collection concentrates not on rule-breaking notation but on extreme usage of notation within the rules, e.g., shortest and longest note durations, most complex tuplet, most independent voices on a staff, earliest use of fff. However, the dividing line between extremes and rule-breaking isn't always clear. My "Gallery of Interesting Music Notation" webpage shows and discusses in some detail particularly interesting examples of both. See also Byrd (2010).

A lengthy table of features of CMN appears in Byrd & Isaacson (2016), and where possible, items below are cross-referenced to entries in that table. Such references are notated as, e.g., "{B&I 8.4}".

Thanks to Edward Auer, Lana Bode, Myke Cuthbert, Noam Elkies, Jay Gottlieb, Jay Hook, Thomas Loewenheim, David Meredith, Craig Sapp, Gabi Teodoru, Joachim Viet, and Micah Walter for their contributions (noted below).

The List

1. Collisions. Too common to be of much interest. A few examples:

1. Ravel: Gaspard de la Nuit (Durand ed.) (almost simultaneous intersections of two beams, two slurs, and hairpin)
2. Scriabin: Piano Sonata no. 3 (Dover ed.), I, p. 49, top staff (double-dotted notes with a stem belonging to a note in another voice between the dots. I'm not sure if this is a perceptual collision as defined in my dissertation; it's more like a "perceptual interruption".)

2. Linear Symbols Interrupted By Other Symbols. Too common to be of much interest. A few examples:.

1. Bartok: 3 Burlesques, Op. 8C, I (barline and staff interrupted by clef)
2. Chopin: Prelude in f, Op. 28 no. 18 (Paderewski ed.) (beam interrupted by clef) {B&I 12.6?}
3. Strauss: An Alpine Symphony, Op. 64, after RM 69 (barline and staff interrupted by clef)

3. Symbols With Highly Non-standard Shapes Or Positions (but minimal or no unusual semantics)

1. Small notes with rhythmic values more-or-less like normal notes, excluding cadenza-like passages entirely in small notes:
   1. Bartok: Mikrokosmos (1926-39; Boosey & Hawkes ed.) Book 6, no. 148 (Dance in Bulgarian Rhythm no. 1), throughout, right hand (triplet of three 16ths, the first full-size & the others small)
   2. Chopin: Prelude in f#, Op. 28 no. 8 (Br+H ed.), throughout, right hand (small 32nd notes regularly double-stemmed with longer normal notes when they coincide)
   3. Chopin: Prelude in d, Op. 28 no. 24 (Br+H, Paderewski eds.), several places (strings of beamed small eighth notes, sometimes starting with a full-size note)
   4. Chopin: Etude in A-flat, Op. 25 no. 1 ("Harp") (Paderewski ed.), throughout, right hand (beamed six-note groups of triplet 16th notes, the first in each group full-size and the others small)
   5. Chopin: Scherzo in b-flat, Op. 31 (Br+H ed.), several places, right hand (passages of a couple of measures of all small notes)
   6. Debussy: Pour le Piano, I, mm. 148-153 (small notes in a cadenza-like passage that seem to act like normal notes, interspersed with normal notes filling each measure's duration)
   7. Ives: Three Places in New England (Mercury ed.), I, p. 6, piano (psuedo-arpeggio of eighth-note dyads with upper note of each normal size, lower note small)
   8. Schumann: Carnaval (Kalmus/Clara Schumann ed.), Op. 9, no. 19 (Promenade), mm. 3-4, 11-12, etc. (small notes with simultaneous full-size rests on the same staff notes, but clearly intended to be played like normal notes, as if "cue" notes but for the same performer)
   9. Scriabin: Sonata no. 1, IV, beginning 52 mm. from the end (small notes that act just like normal notes)
2. Miscellaneous (NB: slurs with many inflection points were formerly listed here, but are now in my CMN Extremes list)
   1. Bartok: Two Rumanian Dances, Op. 8A no. 2 (compound beam)
   2. Beethoven: Violin Concerto (Br+H ed.), II, last measure (very wide fermata over a series of rests)
   3. Berg: Violin Concerto (Universal ed.), p. 47 (one-to-many, many-to-one slurs jumping staves and parts, e.g., clarinet to bass clarinet or bassoon, celli to violins & violas(?)) {B&I 17.6 EXTENDED}
   4. *Berio: Don{de} from Pli selon Pli, p. 15 (slur jumping from clarinet to bass clarinet, to play an out-of-range note) (NB: after 1935) {B&I 17.6 EXTENDED} [contrib. by Cuthbert]
   5. Brahms: Capriccio, Op. 76 no. 5 (International ed.), mm. 7-8 (stem only one space long)
   6. Chopin: Berceuse, Op. 57 (Peters ed.), p.1 (split-stem grace notes, for augmented unison) {B&I 5.25}
   7. Chopin: Nocturne, Op. 27 no. 2 (augmented unison in 2-stem notation
   8. Debussy: Prelude a l'apres-midi d'un faune, piano arrangement by Leonard Borwick, m. 100 (in a 3-staff system, arpeggio sign with notes on the top & bottom staves but not the middle one)
   9. Haydn: Piano Sonata in E minor, Hoboken XVI, I (fermata over nothing, halfway between 2 rests)
   10. Ligeti: Ten Pieces for Wind Quintet (Schott ed.), I (slur jumping from clarinet to alto flute and English horn) (NB: after 1935) {B&I 17.6 EXTENDED}
   11. Verdi: Falstaff (publ.?), p. 203 (accents marks obviously moved to avoid accessory numerals)
   12. Ravel: Gaspard de la Nuit (Durand ed.), Scarbo, p. 41 (slur with 3 inflection points) {B&I 17.17}
   13. Ravel: Gaspard de la Nuit (Durand ed.), Ondine, next-to-last page (slur backing up in the middle) {B&I 17.17}

4. Rhythm Notation.

1. Chord with notes of different durations {B&I 4.28}
   1. Bartok: Sonata for Solo Violin (Boosey & Hawkes ed.), I (double-dotted quarters on same stem as undotted quarters)
   2. Amy Beach: Piano Quintet in F-sharp Minor, Op. 67 (Arthur P. Schmidt), III, last chord, violins & viola (dotted halfs on same stem as undotted quarters)
   3. Brahms: Symphony no. 1 (Henle), I, 4th m. of Allegro, violin 1 (dotted quarters on same stem as undotted quarters)
   4. Brahms: Symphony no. 4 (Eulenberg ed.), IV, last chord, violins & violas (dotted halfs on same stem as undotted quarters)
   5. Chopin: Scherzo in B minor, Op. 20 (Br+H ed.) (half on same stem as quarter; occurs several times)
   6. Chopin: Prelude in Db, Op. 28 no. 15 (Paderewski, Universal, Br+H eds.) (dotted-half on same stem as dotted-8th)
   7. *Dohnanyi: Violin Sonata, piano part (chords with quarter and halfs on same stem) [contrib. by Hook]
   8. Mozart: Violin Concerto no. 3 in G, K.216 (Schirmer/Franko ed.), I, m.42, solo violin (half on same stem as 2 quarters)
   9. Mozart: Piano Sonata no. 6 in D major, K. 284 (Alte Mozart-Ausgabe), III, variation 4 (half on same stem as quarters)
   10. Tchaikovsky: Symphony no. 2 (Eulenberg ed.), IV, mm. 3-4, violins, violas, celli (halfs on same stem as quarters)
   11. Ysase: Sonata for Solo Violin, Op. 27 no. 5 (Schirmer ed.), II ((halfs on same stem as quarters)
2. Note with duration apparently extending across the following barline (cf. "impossible rhythm"). Many of these involve dotted notes where the dotted part of the duration is after the barline.
   1. Bach: "Jesu, der du meine Seele", BWV 78 (Br+H ed.), I, p. 260-61, alto voice [contrib. by Walter]
   2. Barber: Piano Sonata, I, p. 7 (notehead and double dots together before barline) [contrib. by Meredith]
   3. Bartok: Violin Sonata no. 1 (Universal ed.), I (notehead before but dot after barline)
   4. Brahms: Symphony no. 1 (Eulenberg ed.), IV (notehead before but dot after barline)
   5. Chopin: Etude in A-flat, Op. 10 no. 10 (Paderewski, Henle eds.), beginning (it's in 12/8; the left hand plays continuous 8th notes, but the 4th and 10th of several mm. have half-note heads; in the Paderwski ed., they're also stemmed separately with augmentation dots) [contrib. by Hook]
   6. Chopin: Prelude in D, Op. 28 no. 5 (Paderewski, Universal, Br+H eds.), mm. 1-3, etc. (the last 16th of the measure is double-stemmed as an 8th)
   7. Mozart: Piano Sonata in Eb, K.282 (Presser/Broder), III, mm. 48-54, right hand (notehead before but dot after barline)
   8. Mozart: String Quartet, K.465 (Br+H ed.), IV, last page (notehead before but dot after barline)
3. Note with duration arguably shorter than it appears. Usually this is because it would otherwise extend across the following barline but following events in the score make it clear it should not be held for the full notated duration (a type of "impossible rhythm"):
   1. Brahms: Variations on a Theme of Haydn, Op. 56, theme (breve in 2/4 time)
   2. Brahms: Capriccio, Op. 76 no. 1. m. 26, 30 (dotted half in 6/8 time starting a 16th after the downbeat, and tied to a note on the downbeat of the next measure; clearly it's intended to last only 11 16ths instead of 12)
   3. Franck: Prelude, Chorale, & Fugue, Prelude, m. 48 (quarter notes overlapping with 32nd rests in the same voice; clearly the "quarter notes" are intended to last only 7 32nds instead of 8) [contrib. by Hook]
   4. Verdi: Falstaff (Ricordi), last m. of Act I (breve in 6/8 time)
   5. Verdi: Falstaff (Ricordi), last m. of Act II (breve in 2/4 time)
   6. Verdi: Requiem (Dover), last page (breve in cut -- here unequivocally 2/2 -- time)
4. Time signature change in middle of measure {B&I 10.8}
   1. Anonymous (folk song): Wassail Song (typically notated as 6/8 to C or 4/4, but 6/8 to Cut would make more sense: tempo is dotted-qtr = half)
   2. Beethoven: Piano Sonata, Op. 109, I & III
   3. Beethoven: Piano Sonata, Op. 110, III (four times; the passage also has multiple mid-measure key changes)
   4. Beethoven: Piano Sonata, Op. 111, II (occurs at least twice)
   5. Handel: Keyboard suite no 5 in E major, last mvmt (a.k.a. "The Harmonious Blacksmith") (at join between Var. 2 and 3, right hand switches from C to 24/16 in mid-bar, left hand staying in C; between Var. 3 and 4, the hands switch time signatures in mid-bar; and between Var. 4 and 5, left hand joins right hand's C in mid-bar) [contrib. by Elkies]
   6. Haydn: String Quartet in E-flat, Op. 33 no. 2 (1781; Eulenberg ed.), IV (6/8 to 2/4 and back)
   7. Verdi: Falstaff (Ricordi), p. 71 (12/8 to C)
5. Time signature with ambiguous measure duration
   1. Bach: Well-Tempered Clavier, Book II, Prelude in D ("C 12/8" for simple vs. compound equivalents)
   2. Brahms: Piano Trio, Op. 101, III ("3/4 2/4", meaning each measure is one or the other; later, "9/8 6/8", with the same meaning)
   3. Debussy: Preludes, Book 1: Les collines d'Anacapri (State Music Pub. House/Sorokin ed., Dover reprint) ("12/16 = 2/4" for simple vs. compound equivalents)
   4. Rimsky-Korsakov: Scheherazade, Op. 35 (Belaieff/Dover ed.), IV, m. 30ff. ("2/8 (6/16 3/8)")
   5. Ysaye: Solo Vn Sonata, Op. 27 No. 2 (Ysaye/Schirmer ed.), III ("3/4 = 5/4": the vast majority of measures are in 3/4, but a few are in 5/4, one in 4/4, and one, marked "-2-", in 2/4)
   6. Ysaye: Solo Vn Sonata, Op. 27 No. 2 (Ysaye/Schirmer ed.), IV ("2/4 3/4": each measures is one or the other)<\li>
6. One notehead for notes of different duration ending at the same time, and therefore beginning at different times. This is the principal "impossible rhythm" situation of Hook (2008), which gives dozens of examples besides those listed here.
   1. Brahms: Variations on an Original Theme, Op. 21 no. 1 (Br+H ed.), Variation 5 (one notehead for normal 16th and triplet 16th => 1/2 = 2/3; occurs many times) [contrib. by Hook]
   2. Brahms: Intermezzo, Op. 119 no. 1 (1893; International ed.), 12 m. before the end (one notehead for normal and triplet 8ths ending at the same time => 1/2 = 2/3)
   3. Chopin: Ballade in f, Op. 52 (Br+H ed.), coda, next-to-last page (one notehead for normal and triplet 16ths ending at the same time => 1/2 = 2/3; occurs several times)
   4. Chopin: Concerto in F minor, Op. 21 (Br+H ed.), III, mm. 335-36 (one notehead for normal and triplet 8ths ending at the same time => 1/2 = 2/3) [contrib. by Hook]
   5. Chopin: Mazurka in A minor, Op. 17 no. 4.
   6. Chopin: Prelude in C, Op. 28 no. 1 (1836?; Paderewski ed.) (one notehead for normal and triplet 16ths ending at the same time; occurs >20 times) [contrib. by Hook]
   7. Chopin: Prelude in C, Op. 28 no. 1 (1836?; Paderewski ed.) (one notehead for normal and quintuplet 16ths ending at the same time; occurs 6 times) [contrib. by Hook]
   8. Chopin: Sonata no. 1 (1828?; Schirmer-Mikuli ed.), III (one notehead for normal and quintuplet 16ths ending at the same time; occurs 3 times)
   9. Ravel: Sonatine (1903-05; Durand/Dover ed.), III (one notehead for normal and triplet 8ths ending at the same time; occurs 4 times)
   10. Schumann: Bunte Blatter, Op. 99 no. 2 ("Stücklein II") (one notehead for normal 32nd and triplet 8th => 1/3 = 3/8 & 2/3 = 5/8; occurs 4 times) [contrib. by Hook]
   11. Scriabin: Prelude in C, Op. 11 no. 1 (Muzyka (State Music Pub. House) ed.) (several conflicts) [contrib. by Hook]
   12. Scriabin: Sonata no. 7 (Muzyka (State Music Pub. House) ed., Dover reprint), p. 148 (one notehead for normal 8th and triplet 8th ending at the same time)
7. Half notehead with beam(s)
   1. Brahms: Rhapsody in G minor, Op. 79 no. 1 (Peters/Sauer, International eds.) (dotted-half head; occurs many times)
   2. Chopin: Prelude in Db, Op. 28 no. 15 (Paderewski, Universal, Br+H eds.) (half head and dotted-half head in beamed group of 8th notes; each occurs several times, sometimes in the middle of the group)
   3. Debussy: Arabesque no. 1 (Durand ed.) (double-stemmed half head in beamed group of 8th notes; occurs many times)
   4. Fauré: Dolly Suite, Op. 56 (Dover reprint of Hamelle et Cie ed.), Berceuse, Seconda part (half head beamed to 8th; occurs many times)
   5. Ives: Concord Sonata (Kalmus ed.), I (half head and dotted-half head in beamed group of 8th notes; each occurs several times, sometimes in the middle of the group)
8. Non-aligned barlines (these seem to be less common than one would expect; but they're probably more common than these few examples suggest, even up to 1935.) {B&I 7.5}
   1. Bartok: String Quartet #2 (Boosey & Hawkes ed.), I, rehearsal mark 8 (polymeter: 6/8 vs. (3+4)/8, 9/8, etc. with 8th = 8th)
   2. Chopin: "Minute" Waltz, Op. 64 no. 1 (Paderewski ed.), last 3 measures (barlines omitted on one staff)
   3. Chopin: Ballade no. 1 in g, Op. 23 (Br+H ed.), last page (barlines omitted on one staff)
   4. Ives: The Unanswered Question (1908; Southern Music)
   5. Ives: Three Places in New England (1903-14; Mercury ed.), II. Putnam's Camp (polymeter)
   6. Ives: Symphony no. 4, I, p. 3 (1910-16) (polymeter)
   7. Mozart: Don Giovanni (1787; all eds.), Act I Finale (no. 13; ballroom scene) (polymeter: 3/8, 2/4, 3/4. 2/4 quarter = 3/4 quarter; 3/8 dotted quarter = 2/4 or 3/4 quarter)
   8. *Wagner: Gotterdammerung (Eulenberg), end of Act III, pp. 1337-57 (3 mm. of 6/8 vs. one of 3/2; 2 mm. of 6/8 vs. one of 2/2)
9. Multibar rest not in a part of a work for an ensemble
   1. Beethoven: Piano Sonata no. 31, Op. 110, II (in music for a solo instrument)
   2. Kodaly: Hary Janos Suite (Universal ed.), I, m. 75 (in the score of an ensemble work)
   3. Ravel: Gaspard de la Nuit (Durand ed.), Scarbo, mm. 30-31 (in music for a solo instrument)
   4. *Weber: Symphony no. 2, Menuetto, end of both parts ("2" measures each time; in the score of an ensemble work) [contrib. by Viet]
10. Grace-note phenomena
    1. C.P.E. Bach: Concerto in A Major, Wq 168, III, m. 93, flute and viola (fermata on grace note, specifically a long appoggiatura)
    2. Chopin: Mazurka in B-flat minor, op. 24 no. 4 (G. Schirmer/Mikuli ed.), m. 141 (fermata on grace note, but NB this is very likely a mistake by the engraver: it seems clear the fermata should be on the barline immediately preceding)
    3. Chopin: Berceuse, Op. 57 (Peters ed.), p. 5 (grace-note tuplets: several series of three small-note 16ths marked "3"; from the context, clearly grace notes)
    4. Chopin: Nocturne, Op. 15 no. 2, mm. 8 & 9 (normal notehead with one stem and beam to an ordinary note, and one stem and beam to grace -- not just small -- notes)
    5. Debussy: Estampes: Jardins sous la pluie (Durand, 1903) (grace-note tuplets: series of 9 small-note 32nds marked "9"; from the context, clearly grace notes) {B&I 11.14}
    6. Debussy: Preludes, Book 1: La Puerta del Vino; La Terrasse Des Audiences Du Clair De Lune (Muzyka (State Music Pub. House)/Sorokin ed.) (normal notes beamed to grace notes)
    7. Ives: from "Lincoln, the Great Commoner", no. 11 in 114 Songs (grace-note beam whose last note is a normal note in the middle of a beamed group)
    8. Rachmaninoff: Prelude, Op. 32 no. 3 (Muzgiz ed.), mm. 23 & 24 (grace-note tuplets: series of 5 small-note eighths marked "5"; from the context, clearly grace notes) {B&I 11.14}
11. Other
    1. Bach: Brandenburg Concerto no. 4, III, solo violin ("tuplets" that are unambiguous but seem pointless because they're just ordinary notes: 8 16th notes in the time of 8, and 16 16th notes in the time of 16)
    2. Bach: Jesu, Joy of Man's Desiring, arr. for piano by Myra Hess (Oxford) (single notes -- not part of a chord -- on "wrong" side of stem, to show three voices on one staff)
    3. Chopin: Prelude in Db, Op. 28 no. 15 (Paderewski, Universal, Br+H eds.) (7 8ths in the time of 2)
    4. F. Couperin: Passacaille from Pieces de Clavecin, Ordre VIII (pub. 1717) (numerous groups of three 128ths that should be triplet 32nds, and of two 64ths that should be 32nds)
    5. Elgar: Enigma Variations, no. 7 (Eulenberg ed.): time signature of "1", i.e., no denominator (NB: fairly common in early music, even Bach, but extremely rare since) {B&I 10.2}
    6. Hummel: Prelude in B major, Op. 67 no. 1 (Universal/Dover ed.) (tuplet of 8 16th notes in an amount of time that's part of a cadenza-like passage and impossible to define)
    7. Ives: Three Places in New England (Mercury ed.), II. Putnam's Camp, pp. 33, 34, 53 (tuplets crossing barlines)
    8. Ives: Three Places in New England (Mercury ed.), III. The Housatonic at Stockbridge, pp. 65-69 (tuplets crossing barlines)
    9. Schumann: Carnaval, Op. 9 (Kalmus/Clara Schumann ed. & an an unidentified edition on the Web, http://imslp.org/wiki/File:Schumann_-_Carnaval,_Op_9.pdf), no. 6 (Florestan), last 4 mm. (change of meter without notice: the movement has a time signature of 3/4, and it really is in 3/4 until the last 4 measures, each of which has a duration of 2/4)
    10. Schumann: Carnaval, Op. 9 (Dover ed.), no. 1, at Animato and following mm., right hand: "hugely ambiguous" double-stemmed double-dotted quarters [contrib. by Cuthbert]
    11. Strauss: Also Sprach Zarathustra (Eulenberg ed.), p. 64 (tuplets crossing barlines)
    12. Tchaikovsky: Piano Concerto no. 1 (Billaudot ed.), I, p. 25 (measure of two duplet quarters followed by three triplet quarters in C time)
    13. Widor: Organ Symphony no. 5, Op. 42 no. 1, II, p. 20-21, 28-29: notehead with downstem and one beam on its staff (making it an 8th note) but stem extending to the staff below, where it has two beams (making it a 16th note)
    14. Ysaye: Solo Violin Sonata, Op. 27 no. 2, I ("tuplets" that are unambiguous but seem pointless because they're just ordinary notes: 8 32nd notes in the time of 8)

5. Miscellaneous.

1. Simultaneous notes in two clefs on one staff {B&I 8.4}**
   1. Brahms: Piano Sonata, Op. 5 (Br+H ed.), I [contrib. by Auer]
   2. Debussy: Preludes, Book 1: La Cathedrale Engloutie (Durand ed., 1910); occurs 3 times
   3. Debussy: Preludes, Book 1: Voiles (State Music Pub. House/Sorokin ed., Dover reprint); occurs 3 times (with clef in mid-air in front of note on ledger lines)
   4. *Dvorak: Humoresque in F Major, Op. 101 no. 4 (Simrock ed., Dover reprint), near end [contrib. by Hook]
   5. Poulenc: Concert Champetre (orch. reduction, Editions Salabert, 1929), I, p.24 (in an extended passage)
   6. Puccini: Turandot (piano/vocal score, Ricordi), pp. 374, 375, 376, & 377
   7. Rachmaninoff: Prelude, Op. 23 no. 1, 2, 3, 7, 8 (International) (overlapping notes in two clefs on one staff)
   8. Rachmaninoff: Prelude, Op. 23 no. 3 (International ed.)
   9. Ravel: Gaspard de la Nuit (Durand ed.), Scarbo, several places (note(s) on downbeat in one clef, then clef change, then more note(s) that are on the downbeat)
   10. Szymanowski: Piesni Muezina Szalonego, Op. 42 (1918) (ex. in Hewlett & Selfridge-Field, 1994), no. 4 (with clef in mid-air in front of notes on ledger lines)
2. One clef for two staves
   1. Pozzoli: [solfeggio book; but NB probably published after 1935, and arguably not CMN]
3. Movement starting/ending with whole measures of rests
   1. *Ligeti: Lux aeterna (movement ending with 7 measures of rest) (NB: after 1935) [contrib. by Hook]
   2. Liszt: Mephisto Waltz no. 1 (movement starting with a measure of rest) [contrib. by Auer]
   3. Messiaen: Oiseaux Exotiques, last movement (NB: after 1935) (movement ending with a measure of rest)
   4. Mozart: Piano Sonata in G, K. 283, last movement (movement ending with a measure of rest)
4. Non-numeric measure numbers {B&I 7.12} or page numbers
   1. C.P.E. Bach: Fantasia I in F major, Wq 59/5 (non-numeric measure numbers. Begins with an extended free-form measure with systems labelled from 1 to 1h, and ends with a free-form measure with systems labelled from 28 to 28L.) [contrib. by Sapp]
   2. Schubert: Impromptu, Op. 142 #1 (non-numeric measure numbers. The last measure before the two one-measure endings of a repeated section is 81; in one edition, the 1st ending is labelled "81a", and in another, the 2nd ending is labelled "82b"; in both, the measure after the endings is 83.)
   3. R. Strauss: Ariadne auf Naxos (Fuerstner/Dover ed., 1916), pp. 88a, 88b, 88c (non-numeric page numbers. The next page, numbered 89, starts a new scene)
   4. Puccini: La fanciulla del West, vocal score (Well-Tempered Press), pp. 190a-190b (non-numeric page numbers)
5. Non-standard key signatures {B&I 9.1}
   1. Bach: Well-Tempered Clavier, Book I, Prelude in G (sharps or flats not in their usual octaves)
   2. Bartok: Mikrokosmos, nos. 68, 76, 79, 82, 93 (sharps or flats not in their usual octaves)
   3. Bartok: Mikrokosmos, no. 89, 99 (sharps or flats not on their usual notes, i.e., not following the circle of fifths)
   4. Transcriptions of Tu patris sempiturnus es filius and Rex caeli domine, from Musica Enchiriadis, in Norton Anthology of Western Music, 5th ed. (Norton, 2006), vol. 1, pp. 58-59 (B-natural at top of staff and B-flat at bottom)
6. Tied notes with spelling change {B&I 17.1}
   1. Bartok: String Quartet #2 (Boosey & Hawkes ed.), I, mm. 3-4, violin 1 (B-flat tied to A-sharp) (in B & M, 1948).
   2. Beethoven: Piano Sonata in e (Dover/Schenker, *Henle, Ricordi/Casella eds.), Op. 90, II, m. 216 (tied notes in dyad with spelling change on each) [contrib. by Teodoru]. NB: in the Casella edition, this occurs a beat later than in the Schenker & Henle, probably to avoid a diminished 2nd in another voice. But how did Beethoven write it?
   3. Chopin: Sonata no. 3, Op. 58 (Mikuli, Paderewski eds.), mm. 95ff [contrib. by Hook]
   4. Chopin: Scherzo no. 4 in E, Op. 54 (Br+H ed.), m. ?? (chord of D#, Fx, C#, D# tied across key signature change to Eb, G, Db, Eb) [contrib. by Bode]
   5. Fauré: Dolly Suite, Op. 56 (Dover reprint of Hamelle et Cie ed.), III (Le jardin de Dolly), Seconda, mm. 14-15 (C-flat tied across barline to B)
   6. Fauré: song cycle "La Chanson d'Eve" (Heugel & Co. ed., Paris, 1907), Song 1, mm. 94-95, piano RH (C-flat tied to B-natural) [contrib. by Hook]
   7. Fauré: " " , Song 10, m. 15, piano RH (C-flat tied to B-natural) [contrib. by Hook]
   8. *Franck: Piano Quintet in F Minor (Peters ed.), I, about midway between rehearsal letters K & L, piano (the left hand has octave D-sharp tied across a barline to octave E-flat. (At the same time, the cello has E-flat tied to E-flat.)) [contrib. by Hook]
   9. Ravel: String Quartet (International ed.), III, rehearsal mark K, viola (Gb tied across barline to F#)
   10. Ravel: Gaspard de la Nuit (Durand/Dover ed.), II (Le Gibet), mm. 27-31 (a series of A-sharp octaves is followed by one of B-flat octaves, then back to A-sharps, then to B-flats; the last of the 1st three series is tied to the first of the next series)
   11. Strauss: Also Sprach Zarathustra, in the fugue section titled "Von der Wissenschaft" (occurs at least four times at different pitch levels) [contrib. by Hook]
7. Multiply-augmented or -diminished melodic intervals
   1. Brahms: Clarinet Sonata in E-flat, Op. 120, No. 2 (Wiener Urtext ed.), m. 97: doubly-augmented unison (bass line moves directly from F-sharp to F-flat) [contrib. by Hook]
   2. Fauré: song cycle "La Chanson d'Eve" (Heugel & Co. ed., Paris, 1907), Song 1, mm. ??: doubly-diminished third (Cx to Eb) in LH in second system [contrib. by Hook]
   3. Fauré: " " Song 8, mm. 15-16: doubly-augmented unison (G# to Gb) in first measure, RH [contrib. by Hook]
   4. Satie: Vexations, RH, triply-augmented unison between chords 9 & 10 and between chords 26 & 27 [both are B# to Bbb]; between chords 31 & 32 [Bbb to B#]
8. Beams with simultaneous notes/chords with stems up and down
   1. Debussy: Danseuses de Delphes, in Preludes for piano, Book I (Durand ed.)
   2. Ives: song "Thoreau" (Merion Music ed.)
   3. Ives: Three Places in New England (1903-14; Mercury ed.), II. Putnam's Camp, p. 31.
9. Other
   1. Chopin: Nocturne, Op. 15 no. 1 (Durand ed./Debussy), near end (grace note on grace note) {B&I 5.36}
   2. Mendelssohn: Spring Song, no. 30 of Songs without Words (?? ed.), m. ?? (grace note on grace note) {B&I 5.36}
   
   
   3. Tchaikovsky: Piano Concerto no. 1 (Eulenberg, Billaudot eds.; Schirmer/Joseffy 2-piano reduction), I, m. 6 through at least 14 (simultaneous 8va and non-8va notes on one staff)
   4. Ravel: Gaspard de la Nuit (Durand ed.), Scarbo, last page (one 8va sign for both staves)
   
   
   5. Strauss: Also Sprach Zarathustra (Eulenberg ed.) (system spanning two pages, sideways)
   6. Wagner: Die Meistersinger (old Schott miniature score) (system spanning two pages, sideways)
   
   
   7. Haydn: "Farewell" Symphony, IV, Coda (heavy double bars in some staves, single bars in others)
   8. Nancarrow: Study no. 35 for Player Piano (metronome marks qtr = 283-1/3, 141-2/3, etc.) [but NB: this is relatively recent music, and probably not from a respected publisher!]
   9. Schumann: "Susser Freund, du blickest" in Frauenliebe und Leben, Op. 42 (grace chord with arpeggio sign) {B&I 5.28}
   10. Tchaikovsky: Symphony no. 2 (1873; Eulenberg ed.), I - II, timpani (invisible key signature, i.e., flats indicated by an accord only (in IV and perhaps III, accidentals appear on flatted notes); this is common in 18th century music, but not Tchaikovsky! B&I 3.1}
   11. Stockhausen: Klavierstücke I (publ. 1954; Universal ed.) (chords with different dynamic marks on individual notes) [contrib. by Gottlieb]

A Note About "Two Simultaneous Clefs On One Staff"

On the other hand, the "clef in mid-air" of La Danse de Puck and Voiles really is "two clefs simultaneously active" and not "simultaneous notes in two clefs"! The obvious reason for this bizarre notation is to save vertical space. It's interesting to compare this bit of notation with a device that is not too unusual in cello music. E.g., in the Kodaly Sonata for Solo Cello, Op. 8, there are several instances of a low note preceded by a bass clef appearing on a very short staff segment below the (main) staff. [contrib. by Loewenheim] This is easier to read, and far easier to explain in terms of conventional notation; but it does not save as much vertical space.

References

1. Barlow, Harold & Morgenstern, Sam (1948). A Dictionary of Musical Themes. New York: Crown Publishers.
2. Byrd, Donald (1984). Music Notation by Computer (doctoral dissertation, Computer Science Dept., Indiana University). Ann Arbor, Michigan: UMI ProQuest (order no. 8506091); available (in scanned form) at http://www.informatics.indiana.edu/donbyrd/DonDissPageImages.pdf .
3. Byrd, Donald (1994). Music-Notation Software and Intelligence. Computer Music Journal 18, no. 1, pp. 17-20.
4. Byrd, Donald (2010). The Myth of Easy Time Signature Checking. Draft available at http://www.informatics.indiana.edu/donbyrd/Papers/CheckMeasDurVsTimeSigNotEasy.doc .
5. Byrd, Donald (2016). Extremes of Conventional Music Notation. Retrieved June 10, 2016, from the World Wide Web: http://www.informatics.indiana.edu/donbyrd/CMNExtremes.htm .
6. Byrd, Donald, & Isaacson, Eric (2016). A Music Representation Requirement Specification for Academia. Computer Music Journal 27, no. 4 (2003), pp. 43-57; revised version retrieved June 10, 2016, from the World Wide Web: http://www.informatics.indiana.edu/donbyrd/Papers/MusicRepReqForAcad.doc .
7. Hewlett, W., & Selfridge-Field, E. (Eds.) (1994). Music Notation Software. In Computing in Musicology, vol. 9, pp. 167-230.
8. Hook, Julian (2011 December). How to Perform Impossible Rhythms. Music Theory Online 17, no. 4.
9. Rastall, Richard (1982). The Notation of Western Music. New York: St. Martin's Press.