You know, I've never actually sat down and counted the pairs of teats (maybe I should), but they are rumored to have 8-14 pairs of teats (normal rats is 5 to 6 pairs). Which would allow up to 28 young easily. I have just never heard anyone say that without a doubt, their animal had more than 20. Often it's people mistaking 2 litters of two different mothers as one large litter because one female did not show pregnancy very much.

If the female was by herself, I guess it's pretty irrefutable, unless of course someone was being dishonest, which I don't see any reason for when talking litter sizes.