Each witness overview is headed by the relevant source code. Each score in OCVE is given a unique source code as well as a more generalised source descriptor. The codes are either taken from or modelled on the ones in the Annotated Catalogue. The latter uses a tailormade system with individual edition/impression codes 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. abbreviated name (i.e. siglum) of the publisher of the edition (see the list of Publisher sigla).

These elements are respectively separated by a dash (en-rule) and a short hyphen (e.g. 30–1-Sm; see also below). The relevant Witness overview in OCVE shows the edition/impression code for each printed score in the resource.

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 used in the Annotated Catalogue and, as relevant, for printed editions in OCVE:

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 & 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.

Further information about this system is provided in the Annotated Catalogue.

The codes assigned to manuscripts in the OCVE resource use a similar system adapted from this one. In such cases, the first element within the code is again the opus number (or short title if relevant). The second element identifies whether the manuscript is an autograph (abbreviated ‘A’) or a copy (i.e. ‘Copy’ or sometimes ‘Copy/Stichvorlage’). For autograph manuscripts, the third element within the code indicates the type of manuscript, i.e. Stichvorlage, sketch, entry in an album (indicated ‘album’) or fragment. In the case of copies, the third element consists of the name of the copyist, e.g. Fontana, Gutmann and Saint-Saëns. Where multiple manuscripts exist belonging to a single category, these are differentiated by the respective suffixes ‘1’, ‘2’, etc. Examples include 38–Copy/Stichvorlage-Gutmann, 47–Copy-Saint-Saëns, 52–A-fragment, 52–A-Stichvorlage and 61–A-sketch1.

Similarly, the copies of printed editions used by Chopin’s students (Camille Dubois, Marie de Scherbatoff, Jane Stirling and Zofia Zaleska-Rosengardt) or owned by his sister Ludwika Jędrzejewicz are differentiated by the relevant surname appearing in round brackets after the Annotated Catalogue code. Examples include 54–1-Sm (Dubois), 49–1a-Sm (Stirling) and 28/13-24–1a-C (Zaleska-Rosengardt).

Partly for display reasons and partly for ease of referencing and navigation, an additional source descriptor is provided for every score in the OCVE resource, whether a manuscript or a printed edition. Those in the former category begin either with ‘Autograph’, or with ‘X Copy’, where X is the name of the copyist in question. The information that follows thereafter may refer to the type of manuscript (e.g. Stichvorlage, sketch, fragment), but in all cases a short code is given using ‘A’ for autograph, ‘C’ for copy, ‘al' for album entries, ‘sk’ for sketches and so on. These descriptors also contain an abbreviated version of a given copyist's name where relevant, e.g. ‘Fon’ for Fontana. As above, arabic numerals are appended where multiple exemplars exist of certain types of material. Thus, users will encounter such descriptors as ‘Autograph (A-al2)’ (where ‘al2’ denotes a second autograph originally notated within an album, i.e. ‘al’), 'Autograph: sketch (A-sk)’, ‘Autograph: Stichvorlage (A)’ and 'Gutmann copy: Stichvorlage (CGut)’. These descriptors are meaningful only with respect to a specific work, to which no explicit reference is however made within the descriptors themselves. To avoid confusion between two identical entries (e.g. ‘Autograph: Stichvorlage (A)’ for both the Ballade Op. 23 and the Ballade Op. 38), one must therefore carefully note the name of the work which is being referred to, and/or the corresponding source code which does identify the opus number or short title as described previously.

The descriptors of printed editions are similar in design, but they begin as relevant with FFE (French first edition), GFE (German first edition), AFE (Austrian first edition) or EFE (English first edition), with further information to follow about the status of the print within its filiation chain, i.e. whether first impression or corrected reprint. Student/family copies are identified by the name of the user/owner. In all cases the abbreviation at the end of the descriptor provides a useful shorthand for given sources, but again these must be contextually interpreted with respect to the specific opus number or title of the work in question. In these abbreviations numeric suffixes denote not multiple exemplars but rather the successive impression number of the edition in question within the OCVE resource, i.e. 1 = the first impression of the particular edition within OCVE; 2 = the second impression of that edition within OCVE. Note that additional impressions may have been published between a given pair included here (e.g. E1 and E2), but if they do not appear within OCVE itself they have not been factored into the system of identification described above. As a result, ‘E2’ in a given case may not correspond to the ‘second impression’ as identified within the Annotated Catalogue. Users will need consult the latter to discern the status of a given impression within the successive ones produced of a particular edition; otherwise confusion could occur. Thus, descriptors for printed editions such as the following can be found: ‘FFE: first impression (F)’, ‘FFE: Dubois score (D-F)’, ‘EFE: first impression (E1)’, ‘EFE: corrected reprint (E2)’ and ‘EFE: corrected reprint (E3)’. The respective source code will follow in a ‘lozenge’.