And also, if you bring it to an ad or to rolex, they will refuse to work on it. The first rolex I bought was a datejust with a tapestry dial and a sapphire crystal. Being that is was used and I was young, I brought it to rolex on 5th ave here in NYC to have it looked at. After about 15 minutes they came back with the watch and told me that it was genuine but the crystal had been changed from an acrylic to a sapphire and that rolex would not ever service it. I returned it and bought a vintage gmt
Moral of the story is, if there is anything on a rolex watch that is not correct to the case, movement, dial, period, etc, they will not touch it, excluding bracelet. But they never said it was not a real rolex, only that they wouldnt service it because it had aftermarket or non matching parts.