I am not so sure the second ("normal") hatchling from the first clutch is actually a normal. The "alien heads" along the sides are irregular with the eyes run together into bars like the mother. And could that baby be darker than normal? Could the old female's obvious dark color have partly been from age? I have more questions than answers.

Some mutations produce subtle changes from normal. The original owner may have overlooked what you noticed or ignored it.

IMO, a female ball python should be breeding until dead or over 30 years old, whichever comes first.

Good luck with the project.