I would check the movement’s balance spring. If it’s a breget overcoil spring, it’s gen. They haven’t been able to reproduce that yet. Though, I did hear that the 3235 can have a large number of gen parts. Including the balance bridge and spring so it’s getting tougher and tougher to figure out if a watch had all gen parts or not.
What caliber movement are you referring to?
If it’s anything before 3135s, there are no reps of it. 3035s, 1570s..etc were never cloned. So far the only cloned rolex movements are 3135, 3130, 4130, and 3235. 3235s are the ones to watch out for since they can host most gen parts. But if you’re buying any piece before 90s, you’re most likely gonna get all gen movement.
It’s just a matter of knowing what it looks like. You can easily find pictures of those calibers online.
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