Oh, I’m not saying this is LIKELY. I’m just spitballing how it could happen.
Honestly, this sort of organic conspiracy could be robust.
Suppose a particular work A - which is referenced by other works X, Y, Z - is shown to be counterfeit. Does that mean works X, Y, Z are counterfeit? Not necessarily - A could be a counterfeit version of a work that was lost! That would, indeed, be the most valuable work to counterfeit. Take a work that is referenced by other works, find all the references in other works you can, and use that as the skeleton of your counterfeit work. People will eat it up, because they’ve been waiting for it.
New physical evidence, yeah, you’re screwed on that. Especially if you recover an original version of a work that was later counterfeited.