Consensus so far is:
current owner obtained legal rights to do anything other then violate Copyright law once the works were purchased by current owner at public auction, even if they were undisclosed in a clutter of multiple items. Auction parties (sellers) were liable to itemize the items before selling or relinquish all ownership of enclosed items.
Opposing arguments?
Oh. Well, I don't think anyone has enough facts to say
anything for sure.
I can say with some certainty that the artist retains all copyrights in the artwork unless these were expressly signed away by the artist through a license or assignment of rights or other written agreement. If the artist did not relinquish any copyrights in the work in a written and signed agreement, the copyrights remain with the artist. If the artwork was signed and dated by the artist, this helps to prove who created the work, even if the artwork was not federally registered. The artist should, therefore, be able to prevent the person who has the artwork from reproducing the work or using the work for any commercial purpose without permission from the artist.
The ownership of the artwork appears to be with whoever purchased the artwork at auction, unless the person who auctioned the items off acquired the clutter of multiple items illegally. Then
ownership is thrown into question.
But the above is based only on what you have disclosed so far.
For example, there was a case (possibly out of Nebraska, but if memory serves I think it was Utah) where items were hidden or "lost" in a house that was sold and the courts involved in the ownership dispute ruled that the items found in the house by the new owners belonged to the previous owner/home seller and not the new owner/purchaser of the home. So I suppose it is possible, if the artwork was part of a group of items found in a studio/building that was sold, and the purchaser of the studio/building decided to sell what was found, ownership of the items could come into question.
Who are you in all of this? The auctioneer, the buyer of the artwork at auction, the artist? Or are you merely a curious sort?