The printed version of this catalogue employs a concise cross-referencing system to avoid or minimise repetitions of similar or identical material within the source descriptions for each work; one reason for this was to limit the volume to no more than 1,000 pages for practical reasons. As no such constraints exist in respect of the online version, we have retained this system only in the case of simple cross-references, the main purposes of which are outlined in the following indicative list:

• to direct the user to a more detailed explanation elsewhere on the site concerning an impression or a copy (e.g. 1–1b-A&P (GB-Lbl copy), 3–1a-ME, 63–1-BR (Comments)), to a new edition of a work (e.g. 2–1-HAt), to a reference source (e.g. 3–1-ME), to another copy in which one or more parts are missing (2–1-W (US-NYp copy)), and to an im­pression which contains a detailed description of a STP or of a publisher’s catalogue (e.g. Appendix I, Bote & Bock STP DZIEDZINA TONÓW POLSKICH; Appendix II, M. Schlesinger advt MUSIQUE POUR LES PIANISTES DE PREMIÈRE FORCE,|Publiée par Maurice SCHLESINGER, rue Richelieu, 97);
  
• to alert users to other impressions with an identical or similar TP (e.g. 1–1-SC, 4–1-COC, 6/1–1g-W, 8–1-KI, 9/1&2–1c-W), to the re-use of an earlier format (e.g. 2–1c-Hat, 6–1c-BR), or to the fact that two copies are bound together (e.g. 28/1-14–1-W (US-NYpm copy));
  
• to indicate either the presence of separately catalogued orchestral parts and/or solo parts which share a library shelf­mark (e.g. 2–1-HAt, 2–1(Orch)-HAt (A-Wn and PL-Wbfc copies)), or the presence of orchestral parts which do not have an associated solo part but which correspond to a specific impression included in the catalogue (e.g. 21–1-Sm);
  
• to propose the existence of other works which might have been marketed in the same form by citing copies which are differently catalogued but which have similar characteristics (e.g. 27–1j-B&H, 27–2-Ae). 
  

The front pages of many wrappers/‌covers contain a more or less exact replica of an ITP, STP or ATP. Comments are provided either confirming that they are identical (e.g. 27–1c-BR, 45–1d-ME, 63–1-BR) or noting the differences be­tween them, which typically concern the decoration or ink colour (e.g. 8–1b-KI (D-LEm copy), 32/1–1-Sam, 32/1–1a-Sam (A-Wn copy)). Where a single catalogue entry contains several similar or identical wrappers, we provide cross-references to those elements that remain constant. Usually such references pertain to a similar copy within the same cata­logue entry (e.g. 34/3–1-B&H (PL-Wbfc second copy), 34/3–1f-B&H (US-NYp copy)), but in three cases they relate to the title page of another roughly contemporaneous impression (34/1–1a-B&H, 34/2–1-B&H (US-NYp copy), 59–1d-F).