True, technically you could never prove a dominant either; there would always be some miniscule chance you were just lucky with a het. I forget how many only pinstripe offspring he reported but I did the math at the time and was convinced he really did have a homozygous pinstripe.

Last I heard TSK is doing some work with actual records in an attempt to produce and prove a homozygous spider. Perhaps their numbers will eventually be enough for some to make up their mind on what sort of mutation is spider.