Sounds like it the government’s case to prove they were stolen, i.e. that absolutely none of them were sent out for circulation. It will be the heir’s burden that the coins were obtained legally.
The challenge is proving they were legally acquired 80+ years ago. And if they’ve been held that long, how can it be illegal to hold them today?
“Sounds like it the government’s case to prove they were stolen....”
Not for 1933 double eagles. No such coin was ever released for general circulation; in essence, ALL existing examples are automatically stolen, and though they are pretty much just an ounce of gold apparently not much different than any other ounce of gold (.9675 tr oz) if that almost-ounce of gold happens to be in the form of a 1933 double eagle, the government has already gone to insane lengths several times to retrieve the very few examples that exist.