Generally a good idea, but there are edge cases that need to be handled for this to work.

A copyrighted video might not be uploaded to YouTube, in which case you'd have to fall back on the video creation date, which would have to be manually added in their DB (e.g. Hollywood produced movies).

You can also have leaks of videos before their official release. Admittedly a rare scenario that should can be accounted for in other ways (i.e. skip this check if before upload).

> A copyrighted video might not be uploaded to YouTube, in which case you'd have to fall back on the video creation date

Correct, but in this case we know there was no earlier video anywhere, so the only conclusion to draw is that they simply weren't checking the date at all. If the only "source" video being compared with the "offending" video had a newer upload date, the claim never should have been allowed to happen. If there's truly some external video with an earlier upload date, compare to that.