A claim may be widely repeated before its first recoverable source, and a source may be old without supporting the modern version. Pseudohistory and folklore supply separate tests for the story, its attestation and its transmission.
Falsifiability was built for claims you can re-test. Historians replaced it with something else. Bayes handles single events natively and, at one observation, hands back your prior.
Three dictionaries of record carried the wrong origin of OK until 1961. The discipline that eventually settled it had, since 1878, required every exception to be named.