Here is the rear side view of a gen GMTIIC crystal. As you can see, there is AR applied to the back of the crystal (below the cyclops)
On the watch, the AR produces the famous black hole effect over the cyclops
Based on my own experiments a couple of years ago, the AR is definitely applied to more than 1 surface. This is 1 of my test lenses with AR applied only to the bottom side of the crystal
On the watch, the single-side AR does greatly reduce glare, but it fails to produce the black hole over the cyclops
So, as Rolex states in their service literature, the AR is applied to 2 surfaces. Obviously, as you can see in my 1st pic, there is AR on the bottom side of the crystal. The question is whether that 2nd surface is the top of the crystal (below the cyclops) or the top of the cyclops (I suspect the former)?