Though I don't personally believe this, consider the most widely-read book in the history of western civilization still has contested authorship, with many if not most readers convinced God himself dictated the words to the humans who wrote it down. We have no way to prove or disprove that.
I just don't really buy that the set of people who care about that will be big enough for artists to care about signing up for some kind of provenance-tracking regime. Obviously there will be some people in that category on both sides, but I think it'll be niche. I have a hard time imagining Taylor Swift or Drake or whoever is going to start blockchaining their songwriting so that no one can say they used AI. It won't be a big enough segment of their market to care.
(and in fact, the first time Taylor Swift does some big AI-generated video or whatever, all of a sudden a whole bunch of people will suddenly decide they're cool with it)