It's tough to evaluate UV lighting when a basking species has also had natural sunlight exposure. Vitamin D can be stored for up to 2 years so they can easily get through the cold months with minimal or no UV lighting as long as they get sunlight in the warmer months. Another thing to consider is that most reptiles have enough calcium and vitamin D in their eggs to last them for 2-6 months before they develop MBD symptoms. Lots of breeders who say they've never had any problems not exposing their hatchlings to UVB don't realize that most of the hatchlings are long out of their care before MBD sets in.
The general rule of thumb is if a reptile develops MBD before it's 6 months old, test and treat the mother as well as the offspring. She didn't have enough nutrients to put into her eggs.
I know the Philly Zoo started putting their Galapagos torts under UV lighting back in the late 1960s and they have had much better success with longevity, breeding, and disease resistance since. They always did keep them outdoors for about 7-8 months out of the year, but the lighting greatly increased the odds of hatchlings making it to their first birthday.
The Zombie Mama is here!