Unrelated author Y does the same thing, but quoting B, C and X (why wouldn't he? He doesn't know it's fake).
Repeat repeatedly.
Moreover, new ancient works and new physical evdience (coins, letters, inscriptions in stone) have continued to be found, yet somehow they have all remained consistent with the tremendous fraud that was perpetrated 500-600 years ago. To explain this requires a vast, multi-century conspiracy.
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.