I believe, could be wrong, but there is a law in the US where a origional copyright holder(s) can make a claim that he/she didn't mean to sell/throw out his/her artwork and gain back his/her full rights.

I personally wouldn't go down this route because of too many unknowns and that worry one day that there will be a knock on my door looking for his/her cut of the pie (or more formally a cease and desist)