Well, actually there is a lot more to a guitar than wood selection and bracing pattern. One of the benefits of having a handmade guitar, made entirely by one person, is that the maker, over time, learns to use the many variables of wood density and stiffness, as well as the design model, to make guitars that fall within a range of sound and playability. Simply replicating a pattern with good wood (whatever that may be) equals a factory guitar which may be really good, but which is probably much less than a guitar made by a good, let alone great, maker. Jose Romanillos's lecture, printed in American Lutherie many years ago is instructive.
Taking another tack, if I were a dealer, I would be worried about representing a guitar as made by an individual builder when, in fact, it was partly or largely made by others. Using Section_10's facts, with the guitar made mostly by others, but with the famous maker doing some work on the top and signing the label, the dealer is open to charges of violating his state's unfair trade practices act which typically allows for private AND public (i.e., the state's A.G.) suits, with double damages AND the seller paying the individual's attorney's fees. Whatever the culture in Spain, the rules in the States are clear. So, ultimately, it may be a case of seller beware, although I would guess that buyer's buy into the mystique, and people looking for signature guitars may not care as much about who actually made the guitar as who signed the label.
Finally, Mr. Greenberg's comment that, "Regardless of who was building what, their work is indistinguishable," is not exactly confidence inspiring as it invokes visions of factory guitars, which is not what I would guess he intended. Perhaps just an overstatement or poor choice of words.
In the end, all this matters little, but I do feel that accuracy of representation, to steal David's felicitous phrase, is worthwhile, if for no other reason than to respect those makers who really do spend 120 hours building guitars and who deserve credit for their work.