There was a lengthy letter sent to our unit about the new scheme. It explains who's in which group, what each group is entitled to, and why. The main driver for SCLs appeared to be that they don't foul AEA or cause any issues interacting with NVGs or displays (no reflections etc).
If your admin people don't have a copy of it, I think it was unclass so I'll remember to grab a copy and post it here.