Relays don't go back in time to fetch old notes they never relayed originally. If any of those relays had relayed the old notes, there's a good chance they'd still have a copy.

Relays only keep copies of the notes they relay. They don't go out to other relays to get notes they don't have. That's up to your client to do.

To many users just using the default relays in clients. If they added a dozen more random relays, it would help spread the notes out to more relays.