At least in England, Wales, Northern Ireland, the Republic of Ireland, the United States of America, and Canada, knowing that the property was stolen or otherwise obtained by crime is an essential element of the crime.
In Poland the Art. 292 of Criminal Code and Art. 122 of Misdemeanor Code says something like "an item, about which on the basis of accompanying circumstances should and may be suspected that it has been procured by an illegal act" and directly addressed accidental fencing of an item (Art. 291 and 121 respectively address intentional/knowingly fencing an item).
I have no idea how that works in practice but googling "accidental fencing" in Polish ("nieświadome paserstwo") brings up a few results about people who bought cheap stuff online and it turned out to be stolen.
Here's one case like that with a lawyer's answer/opinion if you want to try Google page translate or can read Polish: https://www.eporady24.pl/nieswiadome_paserstwo,pytania,6,64,...
If it's stolen and the government is after you (in this they will), you're toast.
It's not like buying something from e-bay, and it turns out the seller boosted it from a van; that is not your fault.
I think you may have lost track of the thread here. I was addressing this question posed by gtsteve.
> And perhaps in a few generations, the heirs of that wealthy person could sell it on. I don't really know how it works if you discover you've inherited property that was stolen a hundred years ago for example. At what point does it become yours?
It is obviously unlawful to traffick knowingly in stolen goods. It is as serious a crime as the theft itself (sans aggravating factors like use of force or intimidation, especially with a deadly weapon).