There was an article recently about an art gallery in Vienna that carries only top-quality forgeries of famous works. Many art experts have trouble declaring them as forgeries. It was not about legalities but about the talents of many unknown painters.
I thought of that when I heard about the $450M sale....perhaps the original is still somewhere else! :)
Here is the article: https://www.smithsonianmag.com/travel/nothing-art-museum-real-180964918/