npub1wu…0h6ym on Nostr: What would stop publication of an event with an old timestamp using a ...

What would stop publication of an event with an old timestamp using a later-compromised key? NIP-22 I suppose (relay policies)? It wouldn't undo old posts that already were relayed but would allow new posts pretending to be old posts to be relayed. And therefore it would be difficult further in the future to distinguish legitimate old posts from fake old posts, right?