A lot depends on whom the burden falls, I suppose. Proving coercion in an undocumented transaction 60 years on may be difficult. I would be inclined to give the heirs the benefit of the doubt, but the law may specify otherwise.
Well, Liz filed the lawsuit. As I understand it, in cases like these it's pretty well understood that Jews in Germany were under duress from 1932-33 forward. Personally, I wouldn't want to enter a courtroom to prove this wasn't the case in this instance, particularly if I were a public figure. Should have been an easier way to solve the problem.