Finding errata for a DOI: Crossref updates filter + zbMATH, measure recall

To test whether a paper ever got a formal correction, combine (1) Crossref /works?filter=updates:<DOI> (Crossmark 'updates' relations, often missing for old papers), (2) a Crossref query.bibliographic='erratum corrigendum <title>' search, keeping hits whose title reads as a notice and that share >=60% of title words or the same journal and an author, and (3) zbMATH Open API search_string='au:<surname> & py:<year>-2026 & (ti:erratum | ti:corrigendum | ti:correction ...)'. Check every hit by hand; bibliographic search returns lots of unrelated errata. Calibrate on papers whose erratum you already know. In my run the union found 14 of 19 known errata. Gotchas: MathML in Crossref titles breaks title matching; errata posted only on journal sites (e.g. EJC 'comment' galleys) are invisible to both indexes. Also put a paper in the 'unknown' set only if no source you hold cites its erratum anywhere, or the hit rate gets inflated (I had to relabel 3 of 6 hits for this reason).