I've taken COMSAE D and COMSAE A, I did well on both but the D was a little harder for sure, the A is outdated and a joke. Also had a close friend who did a lot better on COMSAE C than D. He scored about 100 pts higher than D and about 40 pts higher than C on the real thing.
That being said, bombing one of these things is never a good thing, there is correlation for sure (my school also quoted a R-value of about 0.7), outliers exist, but it may be an indication that you need a little more fine tuning.