It's a simple concept. It's cash. You lose it, it's lost. It's stolen, it's gone. You find it, it's yours. It's not that hard, even from a legal standpoint. Just like with cash, it usually doesn't matter if you can prove the $20 someone else is holding is yours or not.

I'm starting to get curious why the  OP is trying to use surgical precision with the concept. Sounds like there's some digging going on to get at something.