Each witness overview is headed by the relevant edition/impression code from the Annotated Catalogue of Chopin’s First Editions. Every catalogue entry has a unique code of this type, comprising the following elements:

1. opus number or, for works published without opus number, short title followed in some cases by the key of the work;
   
2. number of the edition, followed by a letter indicating the reprint in question (thus ‘0’ = proof; ‘1’ by itself = first impression of first edition, or at least the earliest published impression to have been located; ‘1m’ = thirteenth reprint of first edition, i.e. fourteenth distinct impression as defined in this catalogue (see also note 2 in ‘Glossary’); and ‘2a’ = first reprint, i.e. second impression, of second edition);
   
3. siglum of the publisher of the edition.

These elements are respectively separated by a dash (en-rule) and a short hyphen (e.g. 30–1-Sm; see also below).

The codes of individual works from multipartite opuses or from editions originally published in two parts or ‘books’ (Opp. 9, 10, 25, 28, 32, 48) contain an oblique after the opus number followed by the number of the constituent work(s) in question – thus, ‘15/2’ in the case of the Nocturne Op. 15 No. 2. Reference is made to more than one work of this type by means of an ampersand (for two pieces) or hyphen (for three or more); thus, ‘33/1&2’ for Op. 33 Nos. 1 & 2, and ‘10/1-6’ for Op. 10 Nos. 1–6. In a few cases, the number(s) following an oblique within the edition/impression code pertain not to constituent works within the opus but to constituent movements within a multi-movement piece (e.g. 35/3&4–2-TR, 35/3–1a-B&H, 58/2–1a-B&H) or to counterparts thereof (e.g. 22/Andante Spianato–1b-W). The first editions published by Chrząszcz, Friedlein and Kocipiński without opus number are designated by codes comprising the opus numbers by which the constituent pieces are commonly known. The same applies to the Deux Valses Mélancoliques brought out by Wildt, Wessel and Ewer. Exceptionally, the opus and/or constituent work numbers are followed by the abbreviation ‘(sep)’ to indicate a reprint in separate editions (e.g. certain Etudes from Op. 25 which originally belonged to Book 1 or Book 2 in Breitkopf & Härtel’s edition).

The examples below illustrate the coding system. Because the CFEO resource tends to include original impressions of the first editions, codes other than those containing ‘0’, ‘+1’ and ‘1’ appear only rarely (e.g. 5–1b-HO, 34/1–1a-Sm, 34/3–1a-Sm):

6–1-Sm

first impression of first edition of Op. 6 published by Maurice Schlesinger (i.e. first edition = ‘1’; first impression denoted by lack of letter following the ‘1’; Sm = Maurice Schlesinger)

6–1c-BR

fourth impression (= ‘c’) of same edition of same opus published by Schlesinger’s successor Brandus

6–2-KI

first impression of second edition of Op. 6 published by Kistner

6–4b-KI

third impression (= ‘b’) of fourth edition of Op. 6 published by Kistner

25/1-6–1b-B&H

third impression (= ‘b’) of first edition of first book of Op. 25 (i.e. Nos. 1–6) published in a volume by Breitkopf & Härtel

25/1-6(sep)–1c-B&H

fourth impression (= ‘c’) of first edition of first book of Op. 25 (i.e. Nos. 1–6) published in separate editions by Breitkopf & Härtel

32–1-W

first impression of first edition of Op. 32 published by Wessel

32–1i-A&P

tenth impression (= ‘i’) of first edition of Op. 32 published by Wessel’s successor Ashdown & Parry

32/1–1j-A&P

separate edition of Op. 32 No. 1 extracted from tenth impression of first edition of Op. 32 published by Ashdown & Parry

37–0-TR

proof (= ‘0’) of first edition of Op. 37 published by Troupenas

70/2&69/2–1-WI

first impression of first edition of Deux Valses Mélancoliques (Op. 70 No. 2 & Op. 69 No. 2) published by Wildt

74/10&1–1-KO
earliest known impression of first edition of songs Wojak and Źyczenie (Op. 74 Nos. 10 & 1) published by Kocipiński

GDC–1-Sm

first impression of first edition of Grand Duo Concertant published by Maurice Schlesinger

PolGm–1-CY

first impression of first edition of Polonaise in G minor published by Cybulski.

After exploring various options, it was decided to preserve the coding system outlined above to avoid confusion between the printed and online versions of the Annotated Catalogue; thus, with one exception, the codes present in the printed version have been maintained in the online counterpart. The system has been extended in order to classify sources discovered after 2010, when the book was published. As a result, new characters – namely, plus signs (+) and asterisks (*) – have been introduced into certain edition/impression codes to designate material that has been added. In these cases, new codes result. The following explanation describes the function of the two additional characters:

• One or more plus signs (+) are used to catalogue newly discovered impressions predating those which previously had been regarded as the earliest impression of a given first edition. For example, two successive impressions of the English edition of Hexameron predating the one classified in the printed volume as HEX–1-CR/M have now been located. In the online version of the catalogue, the earlier of the two ‘new’ sources is therefore classified under ++HEX–1-CRA&B/M and the subsequent one under +HEX–1-CRB/M, the ++ and + respectively indicating successive stages in production. The cases of Opp. 7, 11, 45 & 65 are more straightforward, in that a single impression predating the one that previously was thought to be the first impression has been added, with the result that the new material is respectively catalogued under +7–2-KI, +11–1-KI, +45–2-Sm and +65–1-BR. (The first of these sources, i.e. +7–2-KI, is included in the OCVE resource; the other three are available in CFEO itself.)
• One or more asterisks (*) appear in codes of newly discovered impressions which have been added between two entries present in the printed catalogue. This applies in the case of Book 1 of the English edition of Op. 10, for example. Two successive impressions of this source have been located which chronologically fall between 10/1-6–1a-W and 10/1-6–1b-W; in accordance with our revised system, the first has therefore been classified under 10/1-6–1a*-W and the second under 10/1-6–1a**-W.