Re: Not my field of expertise
> My only question is, once you've "forgotten" about somebody, how do you remember to forget them on a restore?
One suggestion elsewhere that sounds reasonable, is to one way hash their identifiers (email, etc) and store those. The original identifiers can't be recovered, however newly restored records could then be hashed and compared. If any records match, nuke those ones.
On a side note, it would be kind of amusing (not in a good way) to see a hash collision play out through various systems. And if someone's details have a hash collision on one system, there's a reasonably chance they'll also collide elsewhere too.