you missed the part where the parent asked 'who is the authority'

if there are 20 NFT chains, and 10 of them assign ownership to A, and 5 of them assign it to B and the other 5 don't assign it at all - what can we say anymore about the ownership?

all of this public ledger stuff might make more sense if, unlike as is customary, there is a single authoritative chain instead of a 'marketplace' of chains.