I broke a glass drop refractor once, it was at a street lighting contractor as I was searching through their pile of lights, it actually broke fairly easily (I wasn't expecting it to). The only refractor I really don't want to break are the ones for my B2255s since they aren't made any more, all the other could be replaced.
I always trace the refractor pattern of my lights on big paper so if i want an FCO glass for any of my cobraheads, I can go to some glass shop and have them cut a peice of sheet glass.
I broke the glass because I put the refractor door on the roof... Stupid move. And it fell off the roof and hit the ground, shattering the glass. Glass pieces are still on the ground.
And the NEMA label is photo paper with a glue to glue it on.
The drop refractors seem more durable to me, I once dropped a board accidentally on my R47 glass and nothing happened to it.