The proof-of-work part is what I'd use, just for our own small team rather than clients. Last week we changed which language version of a job page is canonical, rewrote titles, and dropped untranslated articles from the index, all within a few days. When impressions shift in a couple of weeks, nobody will be able to say which change did it, because the only record is scattered commit messages. Can an entry be pinned to a set of monitored URLs so you see their before and after around that date?