You are right, NV isn't often used in GT identification. The only times I have seen it used is in conjunction with the Q score. I.e. -- some math programs looked at both the Q and NV scores together to determine placement in an advanced math class.
NV correlates most closely with visual spatial ability or a subtest like perceptual reasoning on the WISC. The kids who score highly on that part of the CogAT are more likely to be good at seeing things from different angles, how things rotate in space, etc. -- architecture, reading upside down, and so on.
NV doesn't really correlate well with achievement in literacy/language arts/reading, though, which is where a lot of GT programs in elementary focus in our experience. That may be another reason why it isn't used in GT identification in schools as often as well.
