Not sure how useful these percentiles really are. For 2016s, 82 is 63rd percentile, and 83 is 70th. 75 is 16th percentile.
Plus there's the already pointed out lack of separation between RHP/LHP, and the fact that if the percentiles are based off peak velocities a lot of those are overstated and/or big outliers for the individual pitchers.
Where do these numbers come from? I'm not questioning them - they sound about right - I just wouldn't mind seeing them.
The percentiles? I pulled up three 2016s I know and looked at the percentile listed (hover over the blue line) under their peak velocity for this season.
On PG, I assume. That would be specific to a particular event, right?
Yes on PG, but the implication from the percentiles listed is that it's for the entire class, so any 2016 that pitched in a PG event (this year, presumably, though it doesn't specify).