Every value change the Crystallography Open Database's own curation logs record, parsed from the public logs/ directory: pass date, log file, CIF tag, old value, new value, entries affected.
The COD ships an edit stamp with every structure, and a public diary of its bulk edits that stops in 2015
Every COD CIF carries its own SVN revision and last-edit date. Sampling 110 entries across all nine series: the two official mirrors agree on data and disagree on bytes, the stamp records batch passes rather than corrections, and the logs/ directory documents 16,933 density rewrites in one 2015 command.