That's NOT the way it works, even under US law. Stolen property is recoverable at ANY point in the chain of possession, even if the current possessor bought it in good faith.
There is NO legal precedent for "Finders Keepers, Losers Weepers," not even if you thrown in a "Neener Neener Pork and Beaner" exigent circumstance.
In other words, the old school ground rights of possession don't apply.
OK, I got this. Stolen is stolen, no matter by whom, or when, right?
But, I have to wonder, who gets to decide if a claim of stolen is valid? And, who speaks for those who are not here to speak for themselves? In some circumstances, that would be a function of governments, right?
What I'm curious about is how the principles might be applied in other situations. Not that "they aren't being applied, don't worry about it.." (today), but whether they could be...tomorrow....
first case: I recently saw a thread about a WWII bringback Luger, taken in the Phillippines from the Japanese. The gun was a Dutch contract gun, issued to their garrison in the far east, taken from them by the Japanese, and then later taken from them by us. Who "stole" if from whom?
A friend I know has actually been approached by some Japanese wanting him to return his "war trophies" to Japan, so the families can have them. Swords, flags, and such. Assume there is no official "permission" document for most of it (never required?)
To date, no hint of any "stolen property" claim, but could they?
Now, in the second case, the guy told those seeking the return that he personally took them from "(ethnic slur) that was trying to kill him", and that they would be destroyed before ... and I understand his heirs are of similar opinion...
Spoils of War are stolen property? I guess what is legitimate depends on what it is, who you are, and when?