I'm trying to remember when the het pied indicator idea first broke on kingsnake. I know it was before summer 2003. And we still don't agree on it!
I have since heard of a case where an imported female with the indicator belly was bred back to a son with the same belly and produced pied. This was a little ironic as I believe the owner was one of the people who didn’t think the marker was useful but noticed the different looking line and inbred it without expecting pied. Still, I wouldn't think it would be accurate enough to regularly pick het pieds out of the wild but I do have a probably wild caught female I’m trying it with just in case.
I'm using a male that was given to me as a 25% chance het pied (the son of a then unproven 50% chance het pied). My male is now actually upgraded from a 25% chance het pied to a 50% chance het pied as his sister proved het pied (indicating his father hit his 50% chance). His markers are pretty extreme and I personally have little doubt that he is a het but am less sure about the females I have big enough to breed him to this year.
Thanks for the report of the results of getting belly striped possible hets from a pair of non belly striped adults. I wonder if this could be something like the spinning in spiders that seems to be directly tied to the mutation it's self but there is some random chance or some unknown environmental factor that contributes to whether or not it's seen. Some report that not all spiders spin and that a non spinning spider can produce spinning offspring and vice versa. Perhaps het pieds have a strong tendency to develop the thick wide lines on the edge of a wide white belly but incubation conditions must be right to produce it so sometimes you get the normal bellied hets. Or maybe the expression is based on other genetics in the animal. It looks like lesser is a separate gene from piebald but some how the presence of a single lesser mutant copy allows the white in a homozygous pied to spread all over the body. So far there has only been one lesser pied but it was also the first all white pied but it's yet to be confirmed that this will happen consistently (I expect it will though). Maybe some "normal" and common gene allows the het pieds to have the starts of pied bellies and het pieds with a less common version of this other gene don't get the belly.