>Will the KC even register litters born this close together?
I have a breed that is mated relatively young - at the second season. Bear in mind that I have my bitches spayed by 4 years old. Average litter size is 1-3 pups.
One of my bitches had a litter at the end of January one year. Her next season was less than 6 months interval (not mated.) At her next season, again earlier than expected, she was mated, and whelped the second week in January. So, not quite the full year between litters. The Kennel Club did not question the registration. However, I don't know if they would have queried this if it was something that happened frequently.
The bitch concerned had 2 pups each time, and was most definitely fit to have a second litter. It may well be a different kettle of fish with a breed that would be mated at 2-3 years old, and breeding past the 4 years that I consider to be too old for my breed.