“I know that Hayes as a hardcopy document handwriting expert would never get qualified to opine on the technical issues relevant to the WHLFBC.”
Hayes is both a document and handwriting expert and has testified repeatedly in that capacity apparently without being disqualified in a Daubert hearing, which he would have been if there were any grounds for his disqualification as an expert. Numerous document experts have pointed to typewriter-related issues which could prove that the BC is a forgery before it was ever placed in a Xerox to be copied.
I see no evidence that Hayes has ever claimed to be an expert in Xerox copier technical issues and I see no evidence that Zullo is relying on any analysis by Hayes of Xerox specific technical issues, if that is what you are getting at.
But hardcopy documents and electronic documents are two entirely different things as far as the expertise involved. To say Hayes would qualify to testify as to the latter because he was termed a "document expert" when he was looking at handwriting issues is like saying an electrical engineer can testify as to a bridge collapse because he once qualified as an "engineer."
Again, this is all entirely academic as Zullo has demonstrated he has no intention on using Hayes at all, let alone pursuing any type of criminal or civil case.