I've only got what's in the archive, and there's not much data to go on. The only two X's in the Blue Grass were Ten Cents A Shine (who came back to run a new top in the Derby) and Hal's Hope (who X'd even worse in the Derby). I'm finding ten "Off" races in the Blue Grass, with two horses getting back to their tops in the Derby (Invisible Ink and AP Valentine), five running "Off" races (Action This Day, Limehouse, Cape Town, Pulpit, and Harlan's Holiday), and three X's (Offlee Wild, High Yield and Sun King). The median performance of these twelve horses in the Derby was 2.75 points off their Tops.

For the 22 others, I find:

3 Tops (14%)
5 Pairs (23%)
4 Off (18%)
10 "X" (45%)

with a median performance in the Derby 2.5 points off their Tops.