So, this case wasn’t covered by CPIA. I assume it was pursued under the National Stolen Property Act (indicated by the language about falsification and that this was a criminal conviction). There isn’t a statute of limitations under the NSPA; stolen is stolen no matter how long ago.

US art museums have moved steadily toward taking both legislative frameworks more seriously. There may still be disputes about how “legal” an acquisition was in the 19th or early 20th c; US legal cases will honor the rules in place at the time of acquisition, not later changes.