Baby rats

Question
I have a rat that gave birth on Halloween (pretty interesting) and after a week of them being born and starting to grow their fur I had noticed a bit of a difference between two of the baby rats,
I have 10 baby rats and only two have it and well they don't seem to be growing any hair, which is weird because all my rats have fur and these two don't seem to grow much fur at all,
like my question is that is it even possible that two rats with fur that mated able to give birth to some babies that could possibly be hairless or slightly hairless?

Also, one more question, before my rat ever gave birth to the babies, my female rat that had these babies conceived on October 1st, and I kept track on everything on her and read that a rats gestation date would be like 23 or 24 days and after 25 days I was getting worried, it didn't seem right, and I was starting to think that her babies might be stillborn or something, and after a few more days she finally gave birth on Halloween which is 31 days. Is it possible for a rat to hold her babies longer?

Answer
Yes it is quite possible to have hairless babies born when both parents are haired. The hairless gene is a mutation so It can randomly occur but because you have two with this it's more likely that one of the parents rats carry that gene for it.

Yes they can go a little longer sometimes but 31 days is a bit too long. She may not have conceived till later. She may not have been in heat when you placed her with the buck then came into heat later and since sperm is viable for 4 days she probably got pregnant then