So yes there is an original keypair that establishes the data. But ones established it can be fixed in a verifiable way. A game client, community of art lovers,

So yes there is an original keypair that establishes the data. But ones established it can be fixed in a verifiable way. A game client, community of art lovers, government agency, social consensus, then recognizes that nft as corresponding to some offchain asset. It cannot be later changed, duplicated, etc without some social consensus to do so. You don't need to trust a third party with control.