To clarify a few queries about bezels/crystals what will fit what won't.
A gen Rolex bezel will not fit directly onto a BP SD without modification. There is however a remote possibility that if you have a really well worn gen Rolex bezel it may just go on. I myself have never come across this.
A gen Rolex tension ring will not fit a BP SD
That said, if you have a worn gen bezel that fits, a gen insert will definitely not fit into the worn bezel and onto the BP case and turn.
A gen insert will fit the BP bezel, but it does need trimming to fit.
There are three suppliers of bezels, Rolex themselves, WSO and Startine (if they still do them). All of these will not fit directly onto a BP SD stock case. Of the two Generic, WSO is closest to gen but again, it does not fit directly onto the BP SD case
Crystals,
Obviously gen is by far the best, it has such clarity along with a second almost invisible chamfer on the top. Excellent as you would expect from OEM
WSO, started off as a good replacement with good shape/chamfers, now it's rubbish, unfinished chamfers that only go 1/2 to 2/3 reds round the perimeter
Clark, a joke over excessive angles, makes the dial look smaller
Startime, poor quality no top chamfer ( and they don't sell the gasket)
J&k about the best at the moment, not a great clarity and the chamfers aren't perfect, but the best there is at present.
Hope this helps