But they also quote a lawyer saying that case law supports the IRS here.
Should have replied to you with this as well, but I'll re-paste it here:
I think this case is factually different from the precedent case law, in that we're dealing with something, as you mention below, that is legal to possess, but illegal to sell. Drugs, stolen artwork, etc., are all contraband items, the possession of which is illegal in and of itself. The black market is the only market available for the transfer of those products. This is a piece of art, legally obtained, the disposition of which is constrained by law.
I'm assuming that your parents are working with a tax attorney and accountant and are taking measures to limit their exposure to the estate tax.So I'm almost certainly fucked. Well it's nice knowing that upfront.