But think of it this way. If you breed that 50% female every breeding season until the 100% offspring is ready to breed that's 3-4 clutches. Averaging 5 eggs per clutch that's 15-20 hatchlings. On average 7-10 of those should be visuals. If none of them are, it's time to give up. You now have a 100% ready to go, and you gave the 50% het girl more than enough chances to prove herself.
I understand what you are saying from a theoretical perspective, but we live in the real world... At the end of the day the purpose of proving out a 50% het is to produce visual offspring.
As I said previously It's possible that a het snake never passes on the gene in question, extremely unlikely, but possible. Technically you can't ever 100% prove that a 50% het is a normal. All you can do is look at things reasonably. 3-4 clutches should tell you what you need to know.