I dont believe there is a great way to tell on the older deployants. The newer style has PANERAI engraved on the backside of the latch clasp, but I have seen some REP deployants that have this feature too. The best way I have found is looking at the screw heads and logos. The gens tend to be made cleaner.
There are some really good reps being made. I would be curious to hear some of the experts opinions.