I've done a bit of rock climbing ... similar thing happened, they started with a rating system where levels
1 = walk down the street
2 = hike in the hills (don't remember exactly)
3 = scramble (need to use hands from time to time)
4 = scramble with fear of death (use of hands, don't screw up)
5 = technical (need rope/gear)
The level fives where then subdivided from 5.1 to 5.9. For some reason, the only technical climbing levels that required any amount of skill started at 5.5, so there were only 4 usable levels to describe a decent climb (5.5, 5.6, 5.7, 5.8 and 5.9) As climbers and gear improved they quickly moved past the first accent ratings and you got this nasty 5.9+ rating, where the 9+ left an infinite possible hardness over the original 5.9 rating. Little Cottonwood canyon was infamous for these 5.9+ ratings. Think Moab scale of 5+. The system later changed to the Yosemite Decimal System which added these ratings above the original 5.9; 5.10, 5.10a, 5.10b, 5.10c, 5.10d, 5.11a-d, 5.12a-d, 5.13a-d, 5.14a-d and 5.15a
The level of difficulty increases once into the 5.10a and above ranges is NOT linear. Think earth quake scales.
I hope these guys did the same thing, but not sure they left enough head room for future growth of tech/equipment if Pritchett is an 8. This statement assumes Pritchett is like the old 5.9 and something super gnarly in BFE is the 5.9+ (i.e. they only left two units to define difficulty than something close to the top of the current scale). If these last two units can somehow be quantified on a non-linear bases it might be ok? Otherwise, 10 years from now, you’ll see 10+