The hublots most closest to gen are the V6, taking a look at a non-V6 movement will be the first glaring thing you notice. Only xx number of V6 models exist, find out what they are, and if the piece you're looking at isn't a v6, theres a chance it could be gen. If it could be a V6, look out for the fat H on the chrono hand, the date window being much closer to the centre as said above, RG and platnium Hubs are heavier in the gen, and SS reps are lighter than gen