The plus/ minus are relative strength/ weakness to you child other scores. It's possible the V was lower than Q & N enough to draw the minus, but that Q & N were close enough to not have a relative strength. I don't know why the website doesn't allow you to enter a score without the plus/minus. It is entirely possible to not have +/- attached to one of the scores. A C profile means the sections V,Q, & N had significant scatter and makes it the results particularly hard to interpret. If the scatter is significant enough, I doubt a Total Composite SAS would be any more help. The SAS on individual sections maybe more informative. It would be similar to trying to interpret a FSIQ with significant scatter. Sorry if I'm just repeating information you already have.
FWIW, I have never like CogAT. It didn't offer a lot of information about my kids and their scores were way off from other testing done. It just seems to be a test with very inconsistent results in the GT population. I wouldn't worry about interpreting to much from this test.
