I agree, my vet shaved loads of Phoebes fur cos she had a nick in her ear, after finding no scar, she opened her up and she was pregnant. I have picked up a stray who still had a spay scar and bald patch though, and she was in an area with very few houses, so we never did quite figure out how she got there, we dont have anyone who would put a cat back in that area, it isn't safe, and she certainly wasn't feral. With her temperament, she is much more likely to be a stray domestic cat.