In my experience, most watchmakers don't purchase spare parts for inventory. If they need something, they'll buy it when needed.
Interesting observation. Well, my own experience and seeing countless watchmaker estates with tons of spare parts being sold off, I think watchmakers buying spares for inventory is actually pretty common. It was common that in the past if you need a stem, you bought a quarter dozen as they used to be sold in packages labelled that way. A major source of vintage spare parts that supply houses like Jules Borel, Casker, etc. carry come from buying up watchmaker estates. I've been in the "back rooms" of some of these places and seen the piles and piles of boxes that they have bought and not sorted through yet. Last year I bought a bunch of spare Rolex movement parts (for vintage, not modern) from a watchmaker who is retiring who has a boatload of stock.
Certainly I don't have everything I need in stock, as I would go broke doing so, but I keep common replacement parts in stock and parts that I know are in danger of being discontinued. When I do my annual inventory, I lay the parts out and snap photos, and then go through them later to update my inventory...here are just a few of the Omega mainsprings I had in stock at the beginning of the year just as an example...
There are many more Omega springs, plus Rolex springs, then ETA springs, etc. Then all sorts of other movement parts, hands, dials, and even cases. Each year I try to keep the inventory from growing, but it's not easy...could buy a nice car with the value of parts I have in stock at the moment.
Now for a vintage dial, I always return replaced parts to the owners, so I don't have a lot of those kicking around - what I have would be from what's left on donor movements that I've bought for spare parts typically. So I do agree that a watchmaker having a specific marker for a specific dial on hand is likely a long shot.
Cheers, Al
