They don't own the stock as I understand it but never received options which they should have and would have been able to exercise. I assume they sold the remainder of the options long ago otherwise they have $3b in NVDA already and probably wouldn't have written this post.

Plethora of reasons, but right to title is not as black and white as anyone assumes. There is no govt ledger that keeps track of who owns what, everything is always subject to interpretation. If you own a home, you likely had to purchase title insurance. If you don’t know what that’s for, look it up. It will give you the same answer to this question.

They do not own the stock, because the options never vested and thus were never exercised. The time to assert that claim was 30 years ago.