The whole question of copying, antiquing, and forging is delicate. My understanding is that JBV was one of the first to artificially age his instruments when making them, so they 'look like' old instruments. But if they are branded internally and signed with a flourish the game would be up the moment the top was taken off, so they wouldn't decieve a connoisseur.
I remember a violin dealer telling me, many years ago, that if someone showed him a Vuillaume 'Strad', he would pick it up and say 1. It is French, 2 It is Vuillaume, 3 it is a Strad copy, in that order, even though Vuillaume was presumably trying to make it 'exact'. Which led me to believe that it is the things we take for granted when making something rather than the things we are trying to copy that give the origin away.
Re Collin-Mezins. Charles Jean Baptiste Collin-Mezin violins might have sold for 400 - 500 francs back then [based on prices in the Bernardel/Caressa and Francais ledger https://archivesmusee.philharmoniedeparis.fr/en/gand/home.html ] which in today's money would be about $2,000-5,000 depending on whether you price as currency [lower figure] or gold. So they are probably worth [roughly] about the same now as then, whereas JBV's are worth 20-30 times more.
JBV would be DELIGHTED that we are still talking about him in this way. A Strad would in JBV's time be about 150 years old, as JBVs are now. Does the age of the wood have something to do with it? I read that JBV did some heat/chemical treatments on some of his violins, and made some out of already old wood. Ole Bull even brought an old piece of spruce from Norway and made himself a new-old violin in JBV's workshop. JBV had great technical curiosity. But he was also a good businessman. He sold a ‘Guarneri del Gesu’ viola for 4,000 francs in 1874 which had had its f holes 'adjusted' not I think by JBV himself.