I would think that its simply proven when its proven. If you have a abnormal looking snake and bred it to a normal and produced a litter of half norms and half with the trait i would guess that you would have proved its genetic and polygenic at the least. If you were then to breed two of them togther and produce 25% norms 50% with the trait and 25% super appearing animals then you can be pretty confident that it should turn out co-dominant. If one of those supers is bred to a normal and produces a litter of 100% with the abnormal trait then you proved its co-dom. Its a morph.
If you bred an abnromal snake to a normal and produced a litter of all normal appearing animals, but then bred them together and produced somewhere around 25% showing the abnoraml trait then i would say you proved its ressesive. Its a morph. I guess the biggest problem is that these genetic percentage equations don't prove to be exact but rather estimations. Not always acurrate which can cause problems.
And i'm speaking my personal opinion of whether or not "I" would purchase the snake as a morph rather then stating the actual standards the top breeders go by becuase i don't know them. Of course id never have the money to purchase one of these fantasy snakes im talking about but hey... i can dream.
-----
2.3 Bearded Dragons
1.0 Pastel Ball Pythons (NERD Line)
0.0.1 Water Monitors
1.1 Pastel Red Tailed boa Het. for Albino
1.1 Yellow Ackie Monitors
And Counting...