Very good questions.. Gotta give AmPit13 Props!! :roll: It's not a good idea to push your dog until at least 1 and 1/2 yrs and really old school rules dogs weren't even really considered until 2, some young hot dogs turn cold and vise verse, gotta let the dog come into full maturity. Undershot jaw is not wanted but your not gonna ever get rid of it, its old world pit dog and I don't mean EngBulldogs.. I've seen the most picture perfect lines have it resurface again and again with this breeding or that breeding.. culling pups and sterilizing dog with undesired traits is the only way to isolate, but some of the gamest dogs have had a slight undershot jaw.. I've seen a whole litter of dogs with tight scissor bites, a couple undershots, and one pigmouthed (overshot jaw) dog. Culling is neccessary for extreme cases, the dog will suffer.. In general I wouldn't stress it.
For any novice APBT owner, spay/neuter, no questions asked. Know your breed, know your dog, and get to know the ethics of registries and renowned breeders.. Then get you a dog you want to breed.. Thats JMO, it prevents undesired characteristics and undesired dogs.