The ISBN was invented in 1970. Your books don't care

The ISBN, created by statistician Gordon Foster in 1965 and standardized as a 13-digit code in 2007, was designed for mass-market, offset-printed paperbacks and now dominates modern cataloging software, which treats the field as primary metadata. Early-modern works lack ISBNs and rely on specialist identifiers such as ESTC, VD16-VD18, USTC, GW, and historic bibliographies like Brunet or Graesse, which remain essential for rare-book trade and scholarly reference.