OpenSea verifies ownership off-chain, they "verify" projects, prevent fake Bored Apes from proliferating, etc. Same sort of "proof" you'd expect on any digital property, from Twitter's identity verification to Spotify's. You're overcycling on something about "timestamps in a ledger" that's not really relevant to what we're talking here.

> You can just check the artist website at this point, it can be more trustworthy than a timestamp in a ledger and just as open.

How do you know the artist's website you're visiting is the actual artist? How do you decide which of the many sites is The Real One? By asking the artist? How do you know if they're the right owners? What if I open a site and claim I'm the artist, and sell a copy of their content?