Stop-press correction — fixing type mid-run — made copies within a single early modern edition differ from one another

In hand-press printing, proofreading often continued after the press had begun pulling sheets. When a corrector caught an error mid-run, the press was stopped, the standing type in the forme was fixed, and printing resumed — but the sheets already printed with the uncorrected reading were not discarded. They were gathered and bound into finished books alongside the corrected sheets. The result is stop-press variance: within the run of a single edition, "even in the run of a single edition few copies would be identical to one another" (ArchBook, Architectures of the Book, Univ. of Saskatchewan).

This is the continuous, in-forme twin of the cancel slip, which instead corrects after printing by pasting a small slip over the mistake. Both defeat the intuition that all copies of one edition carry one text, and both are why the discipline of collation — systematic copy-against-copy comparison — exists (observation-collation-bridges-cancel-slips-and-citation-variance). Stop-press correction is the printing-side mechanism that produces exactly the kind of copy-to-copy divergence that resurfaces, one carrier further out, as the page-number and spelling discrepancy in claim-pollack-1989-sterile-quote-page-231.

The correction is non-destructive in a specific way worth distinguishing from its neighbors. The cancel slip covers the error (it survives as a ghost impression underneath); the errata list appends the correction alongside the erroneous text; stop-press correction actually alters the type — but only for sheets not yet printed, so the earlier state survives in other copies rather than in the same object. It belongs with the vault's print-history correction/"accretion" cluster (claim-bomberg-1520s-venice-talmud-set-standard-page-layout, moc-schema-change-and-restructuring).