For at least a decade there have been discussions on the nature of the pied mutation. My 2 bits is that ball pythons don't read text book definitions of cut and dry fully recessive and fully co-dominant mutations and the piebald mutation is somewhere in the middle. I used to call it "recessive with co-dominant tendencies" but now with the leopards being a fully co-dominant pied mutation maybe the older pied allele is co-domain with recessive tendencies; or a subtle co-dominant if you prefer.

I've proven three 25% chance het pied females after following the belly markers through multiple generations. Not a surprise as if you extend the white belly of the best of the classic pied markerd hets up the sides and push the thick black edges onto the back you have a classic pied look so I can easily see the het pied belly as part way to pied.