Actually ... yeah, they do school by size (year class) alot of the time. Been hearing alot of GRL reports of catching a bunch of shorts, with only a few keeper size in the mix. There's plenty of big Crappie in that lake, though. They're probably out along the channels, in deeper water, still following the Shad schools.
Green River Lake also seems to be one of those lakes that goes thru a cycle. A couple of years of sub average to average sized fish caught .... then a banner year of slabs ... then back to the sub/average size fish.
Post turnover fishing can be tough, too. It scatters them out, through the depths. With the thermocline gone, and the water/oxygen mixed throughout the depths, they're no longer confined to the upper layers of the water column. Turnover can also be a stress factor to them, until things settle down & they get back to their early Winter routine.

... pappy