That makes sense on the undescended testicle thing. It's the same way in humans... it lowers sperm count, but it's still possible to have viable sperm. That's not really applicable to my situation anyway. I thought he had an undescended testicle, but I remembered that they sent us home when we tried to fix him the first time and said to come back when it drops, which is what we did.
On the six weeks thing... we kept them separated for 8 weeks pre-neuter and four weeks post-neuter (I learned my lesson on that one the first time). He was fixed January 2. By my calculations, if she got pregnant even at the end of February, she would have already had the kittens or she'd be ready to pop.
Is it possible to leave any spermatogenic tissue inside? That's my next question. I guess I could look that up.
I don't think she's preggo, but she is bigger and eats more (strangely familiar behaviour). :para: She can't handle the anesthesia, so the vet said I should be okay not spaying her as long as the males in the house are neutered (which they are!) in case you guys are wondering.