Over many years in this business, I have accumulated an inventory of tens of thousands of crystals. Plastic, glass, tempered mineral, you name it. I once bought out a bankrupt material wholesaler's inventory of about 30,000 antique fancy shaped glass watch crystals. I still order thousands of crystals annually for watches! Of course, that includes modern watch crystals as well. My answer is, if you are going to build an inventory, build it in ROUND crystals for open faced and hunting cased pocket watches of all sizes, and round ones for wrist watches. And unless you can luck out and buy an inventory for not too much money like I did, buy the fancy shapes as you need them. Even at that, you'll find the well equipped supplier unable to supply the odd one, and you'll have to have him cut one to fit.