Agree with the caveat and would put it more strongly. In practice credentials survive almost nothing. Screenshot, re-upload, crop, any platform that re-encodes, and they are gone, which is to say they are gone from most of what you actually encounter.
So it is a signal that works beautifully inside a workflow where everybody is cooperating and barely at all out in the open. Useful when present, and worth checking because it costs ten seconds. Just never read missing as suspicious.