Seems like a really simple fix. Serialize the watch and the case back and the movement. The movement need not match but since you have complete control of the supply chain you can track what movement goes into what case with what case back.

Alternatively you can just state that the watch is the case back. You have to put all the anti counterfeit stuff into the case back instead but then you just control everything that way. Sort of like the aircraft is the placard. If you have an aircraft placard you can rebuild an entire aircraft around it and it would still be considered the same as the original unit.

It sounds like Rolex likes the idea of the watches not actually being traceable. There is no need for blockchain or anything fancy a ledger or database owned by Rolex would work well enough. Ownership can be transferred at your local Rolex dealer where they verify authenticity for a nominal large fee type of deal.

Seems like a watch is a pretty poor black market currency because they are knocked off so often you would have a hard time verifying authenticity and most of the value is in the authenticity. I guess sufficiently discounted they might work in volume.