I'm by no means an expert on the yellow belly thing and haven't seen one (I don't think) but apparently there is more to it than just the color of the belly. I believe there should be no black and the belly and the black should tend to group around the edges of the belly sort of like a bloodred cornsnake. There may also be something about the dark pattern fading low on the sides and other factors to distinguish the real thing.
Details are pretty sketchy and I'm not sure that anyone knows all there is to know about them yet. Yellow bellies might or might not relate to other mutations associated with white snakes (phantom, platy, maybe even mojave). I think the speculation is that some of these may be the heterozygous forms and the Ivory/Leucistic may be the homozygous.
It’s sort of ironic that after years of people getting scorned for pointing out subtle variations in snakes for sale all of the sudden we have stumbled on some subtle variations which appear to point out gene carriers for mutations which are much more stunning in the homozygous form.
Regarding the slow (over the summer or perhaps even over years) leak of information to the general public regarding this project I'm frankly a little disappointed that it’s taken this long and is still this sketchy. With such big bucks and tough competition involved I guess I can understand it. For good or bad these aren't cornsnakes and aren’t just for the fun of it. The big bucks drive the productions to get these slow producing snakes out as quickly as possible (probably would take forever at corn snake prices). Unless I'm ever in the position to have a new morph all my own I guess I can't really say what I'd do.