The paints don't breed true is because of other genes than the spotted gene. You are dealing with a known dominant gene (Slate - D) that exhibits the "it doesn't breed true" case. I have seen no information that indicates any other reason for them to not breed true when they all turn out as...
Just have to wait and see when he lists the color genetics for their color varieties. Thought maybe I could play with the color calculator to get an idea of what they are but he does not have painted gene as an option.
Guessing:
Dominant Slate Painted (BB cc Dd EE NN PnPn RR SlSl spsp)...
It is listed as a recessive gene. The Nebraskans may have had something else going on. The ones or at least most of the one's listed have been with the dominant Slate gene.
"Eighth is the
Spotting site:
Sp for (normal) and sp spotting (mutation)
The turkey variety known as the Nebraskan carried this gene."
Feather Color Genetics