Alright, I oversimplified and thus stand corrected... Since sunglow is a physical description and not a genetic trait, as long as the snake looks like a sunglow, it is a sunglow. The problem is, it can be difficult to tell as a hatchling how a cornsnake will turn out as an adult. And since some breeders use different recipies to make sunglows, sometimes they don't mix well. Line-bred crossings aren't as predictable as genetic traits and only generalizations can be made.
You still cannot have a cornsnake 'het sunglow' (nor het miami, okeetee, upper keys, candycane, or any other line-bred morph).
-Kat