Other tells...
-21J - ticks at 6 clicks per second, swiss and asian copy eta at 8 clicks per second (closer to gen). So on the 21J, the 2nd hand sweep is not as smooth. I can see this but the general public won't be able to tell the difference.
-Lume - most rep lume sucks. Gen lume will glow after just a few seconds in sunlight. This is not an obvious tell, but one none the less.
-SEL (solid end links) should fit tightly against the lugs. Sometimes reps get this right sometimes they don't. Also should not have a gap b/t the SEL and the bracelet. Some are good and some are quite bad.
-height of the crystal can be a tell as well.
-Rehaut has already been mentioned.
-bezel teeth. Most of the reps look bad. not scalloped enough and the teeth aren't sharp enough.
-date font - can also be a giveaway, but the reps are getting better at using the proper font.
-bezel pearl. Most are just plain wrong. You'll have to modd em to get the right.
-bezel insert - should sit slightly below the bezel rim. most sit slightly above.
You should do a search and read up on By-tor's, BLK, fakey, and other's reviews on the submariners. You can learn a lot from those guys.