One interesting thing about the Poles wanting a rare rifle back is their claim it is a national historical cultural treasure. What we apparently have is a rifle designed by a Pole (rare in itself), made in extremely limited numbers (150?) issued to their police forces (the Polish military was equipped with Mausers).
HOW, exactly does a limited production run (apparently ended by the war) of any firearm make it a national historical cultural treasure? A historical artifact, certainly, but a national treasure? This was (apparently) NOT a military weapon, and while the individual police may have fought against German attackers, a surviving example of a rare (experimental?) rifle isn't ordinarily considered a "national treasure" without specific documentation of the unique circumstances of the individual rifle.
To me, this seems like one government asking another government to literally steal a citizen's property using a legal claim based on a tenuous classification of the artifact by the govt that wants it.
When it comes to art, or things like pre-Colombian artifacts, or anything actually worth a quantity of money, govts tend to be greedy, and the rights of the current owner or discoverer get trampled more often than not.
I see it this way too.
First, Poland really has no right to say it was stolen, as during a war, and per treaties, weapons are confiscated or seized, and a good majority are destroyed. The treaties even allow for war trophies.
Second, the treaty of 1907 does not list any weapon as being protected, only art treasures, statues, and places of science and learning such as universities, etc, though they may be owned by the state. Here, these were specifically protected from being war trophies, but nothing else.
Everyone who signed the treaty understood this, and weapons, any of them, or anything pertaining to the military is exempted, and fair game, even the buttons on their dress uniforms if we get picky about it. This, especially in Europe, as they have been collecting war trophies for thousands of years, including weapons, flags, etc. They have huge galleries of trophies in several countries in Europe. Plus, when you read the treaty, it really didn't have much teeth to it, and only gained a small amount extra in the 50's, when some additional language was added, but nothing that happened before was grandfathered in.
Now, you have Poland hollering it was stolen by the Germans, who declared war, with an army who invaded them, and seized their weapons, which is legal in war, but Poland likes touting the word stolen. That wouldn't pass muster in an international court, especially using this treaty. Also, that is between them, and its funny that Poland has never said anything about Germany concerning this, since WWII, and until now. Why didn't they demand that Germany give them back all of their 'stolen' weapons?
If the gun made it to the US, the way the owner says it did, in that it was taken from the Germans, it was a legal seizure of a weapon by US military code, and can be seen in that code as late as 1994. So who's at fault, it sure isn't the owner?
I have an idea that Poland chose now, over who we have as president, hoping he will look the other way, since its a gun, and give them something for nothing. If it does make it to court, which it should, as the NRA is paying for an attorney, then Poland is going to have to cough up the cash for court, and it may well cost them more than what the rifle is worth.