I've looked through several genetics books. There may be as many as 4 intermediate categories of inheritance or as few as one. I'm defining an intermediate category of inheritance in which the heterozygous phenotype can be distinguished from both homozygous phenotypes.

Here's a source that has only one category:
ghr.nlm.nih.gov/handbook/inheritance/inheritancepatterns

"In codominant inheritance, two different versions (alleles) of a gene can be expressed, and each version makes a slightly different protein (illustration). Both alleles influence the genetic trait or determine the characteristics of the genetic condition."

How reliable is the missing scale on the head as a mark of the heterozygote? If more than 5% of the heterozygotes have full scalation, then I would call scaleless a recessive mutant gene. The missing scale character would simply be a het marker.