Only just caught up with this thread. So many times in the past we have been called out to take in a female who is about to give birth in a garden and it has turned out to be a male with an 'hereditary pouch'.
I remember once very early in the morning I received a phone call from a lady who said she had seen a car hit a cat and had taken it inside her house so it does not go in the road again. She said she could see no signs of external injury but she said the cat was pregnant. Immediately I went to her house a few miles away. There was no obvious sign of injuries but as we all know we cannot take the risk that the little one did not have internal injuries. Anyway we got talking (as you do) and she gave me all the reasons why she could not keep the cat although she would love to. I cannot remember what the obvious signs were that the cat was hers but by then I knew it was. (I always ask in these cases, if the cat is yours please tell me as I will still help you but I will be able to find out more about the little one and its likes and dislikes, she denied all knowledge) She then signed over the cat to Cats Protection. I then picked up the little one as I was leaving she said will you let me know when it has its kittens, I replied , oh! It won't be it's a boy. Immediately she said I will keep it then if it is a boy, but I advised her that she had now signed it over to me and its owner may turn up and even if they didn't then because of the reasons she had given why she could not keep it, then it was in her interest to re-home it. Her face was a picture. On the way home I called in at the vets just to be in the safe said and the vet confirmed that the little one had certainly not had a meeting with a car. No surprise there then.