Can you describe what the male looked like? I have a tortoiseshell who's all crooked. Her paws are twisted inward, her tail is shaped like a spring, her rear legs are longer than her front legs. She's all weird. Now I'm wondering if she has extra stuff like a vertebra too. Does your male cat looked overall normal despite the extra vertebra?
They both looked normal and where quite beautiful cats actually.
We only found out their health issues from exams.
We had a cat with a "pig tail" as in his tail was shaped like a pig's and couldn't straighten out. The vet said it was some relatively common birth defect and wasn't a major issue.