Each catalogue entry is designated by an ‘edition/impression code’ 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.[1] 
   

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 this coding system:

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.

The situation is more complex in respect of constituent works within an opus for which multiple en­gravings were prepared and which were published both separately and as part of the entire ‘set’. For such works (e.g. Kistner’s Op. 9 No. 2 and Wessel’s Op. 25 No. 1 – see below) the edition numbers do not desig­nate successive editions as such but rather relate to the version of the composite impression from which the relevant engraving was extracted. For the Nocturnes Op. 32 published by A. M. Schlesinger and the Posthu­mous Works brought out by J. Meissonnier fils and A. M. Schlesinger, two independent series of edition numbers are required – one for separate editions, the other for composite versions. This arises with regard to Op. 32 because of the comparatively late publication of the version containing both nocturnes, while for the Posthumous Works it has to do with the relative rarity of the composite volume. The following list provides relevant examples:

9/2–1d-KI
second engraving of Op. 9 No. 2 published by Kistner, extracted from 9–1d-KI (i.e. first impression of entire opus to combine this second edition of No. 2 with first engraving of the other two nocturnes)

25/1–1d-W
second edition of Op. 25 No. 1 published by Wessel, extracted from 25/1-6–1d-W. The new engraving of this etude appeared for the first time within 25/1-6–1a-W, but because the publication date of the separate edition is closer to that of 25/1-6–1d-W, the extraction in question corresponds to the latter (hence the ‘d’ in 25/1–1d-W).

32–1-Sam
earliest known A. M. Schlesinger version of Op. 32 as a set containing both nocturnes. Notwithstanding the ‘1’ in the edition/impression code, this contains the second engraving of each nocturne.

32–3-Sam
third complete version of this opus published by A. M. Schlesinger. It combines the fourth engraving of Op. 32 No. 1 with the third of Op. 32 No. 2.

Posth–1c-Sam
fourth version classified within this catalogue of the volume containing the Posthumous Works (Opp. 66–73) published by A. M. Schlesinger. This contains the fourth engraving of Op. 66 and the second of both Op. 69 and Op. 71 No. 1, along with the first edition of the remaining works. Nevertheless, be­cause more than half of the volume was prepared from the original plates, its edition/impression code retains the ‘1’ of the first edition (for further discussion see ‘Second, third, etc. edition’ in the Glossary).

After exploring various options, we 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 (described below), the codes present in the printed version have been maintained in the online counterpart. We have extended the system 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 & 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 and +65–1-BR.
  
• 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.
  

Codes of newly added impressions which postdate the last to appear in a given entry in the printed version of the cata­logue follow the normal sequence. For example, the code 19–1d-PE has been assigned to an impression of the Bolero Op. 19 which was published after the one classified under 19–1c-PE in the 2010 book.

Although our revisions of the coding system have generally allowed us both to preserve the original classification scheme and to accommodate new entries as described above, there are some exceptions. First, the edition/impression code of a single source has had to be revised: originally catalogued under 10–1-Sm, this now appears as 10–1*-Sm. Secondly, the discovery of a true first impression of the German first edition of Op. 11, featuring a title page with decorative background in colour (see +11–1-KI), has resulted in the reclassification under 11–1a*-KI of the copies originally in­cluded under 11–1-KI. The production sequence implied by this reordering of the material is entirely logical, given that the copies with decorative title page (+11–1-KI followed by 11–1a-KI) would certainly have appeared prior to those featuring an ordinary title page (printed in black without decorative background). The result, however, is that, exceptionally, the code 11–1-KI, which appears in the printed version of the catalogue, is omitted from the online counterpart. In addition, we have modified the code for the Fantasy-Impromptu Op. 66 from 66–1f-GE (as in the 2010 book) to 66–1f***-GE to reflect the revised classification of the Posthumous Works (Opp. 66–73).

[1] For a comprehensive list see sigla see Sigla of publishers.