I think what you said only applies if the current owner is the person who stole it (or knows it's stolen). if they gift it to someone else who thinks it's legitimate, then that new owner is allowed to claim it as theirs until/unless someone else comes forward and says the first person stole it from them. in which case they now know it's stolen and either they return it or live with the guilt. at this point what you said about ethics/legalities now applies