I think they do upgrade fellowships to CGS, as people on other threads have mentioned being bumped up from a Doctoral Fellowship to a CGS. I tried calling re: the waitlist (I'm #3 on the waitlist for committee 1b) and got the runaround: they absolutely won't comment on the likelihood of receiving funding of you're on the waitlist. They did, however, tell me I shouldn't expect to hear anything "before Fall, at the earliest."