First to understand breeds you need to understand that our current breeds came from natural races of dogs - man did not create dogs...he only created the purebreds that he made from natural races of dogs. Current purebred dogs are fairly new.
Basically we humans are races, we adapted and evolved to suit our environment (Eskimo's, Pigmy's etc.) the only difference is each race evolved to suit it's environment. For a human to become a purebred or a breed you would need the assistance of Hitler or follow the dangerous breeding of the royal family.
So, by realizing that all of our current man made breeds came from natural races of dogs it is quite easy to see where all the confusion of the ancestry of our current purebreds come from. In the day of dog fighting as a sport man used dogs that had enhanced motor patterns and the full sequence of predatory motor patterns...it's quite interesting to know that natural dog breeds have the full series of motor patterns but not enhanced like some of our working groups. Anyway, back in those days man either just let their dogs breed naturally (for example the transhumance on their biannual migrations...you had people moving sheep with their dogs for hundreds of miles which allowed their dogs to mate with village dogs along the way.), or they took the best dog (the winner and bred to the another top fighting dog...perhaps even carrying over some specific motor patterns developed).
So, understanding that there were natural species of dogs man then started realizing their worth...but, they still were not breeding as we do today, they used a huge gene pool instead of small gene pools that we do today.
So, basically the APBT came from a race of dogs perhaps looking a little bit like the current APBT's...the dogs were good at fighting - their behavioral conformation shaped the dogs into the current look they have ...when the kennel clubs came along they took the "look" of those fighting dogs and tried to recreate the same look without the enhanced predatory drives to make nicer pets. So, therefore you have tons of dogs that come from these races (not purebreds)...in order to create a purebred dog you have to set a standard and a look, this involves separating a few select dogs from the mass population and line breeding and inbreeding to set a standard look. All of our current purebreds have inbreeding in their lineage. Once you have set a standard look and behavior for so many generations you can then approach the kennel clubs and asked the breed now be recognized. I could start a new purebred dog within the next 2 years if I wanted to. So, this is how you create a purebred, a purebred dog comes from races of natural dogs which have been sexually isolated from the great population. That is why you can have so many different purebred dogs and mixed breed dogs that look like a certain group...and sometimes mongrels may be the direct descendants of the orginal fighting dogs (which were races, not purebred or breeds) and have no purebred lineage in them at all...keeping in mind that purebreds are fairly new. Sometimes a person will see a dog that looks like an APBT, but, will state it is not an APBT...but, this dog may come from the same natural race of dogs that the current Staff's, APBT's and other bull breeds come from.
So, this brings us to the working dogs and dogs used still for dog fighting. Most working dog breeders realize the harm and damage a kennel club does to a breed of dog over all. So, some breed clubs will drag their feet and not allow their breed to be recognized...this is what happened with the border collies. A few years ago, perhaps more than that...people who work their sheep with border collies waged a campaign against the registration of their breed by the American Kennel Club. Because showing eye is a genetic trait, it can be selected against, and if border collies are going to be bred for shows and as pets, breeders are going to have to get rid of the eye. This is basically the same for the APBT, if they are recognized by the AKC the breed club is afraid they will ruin the enhanced drives that make them good fighting dogs. I've talked to a few border collie breeders who have caught judges putting up poor species of border collies in the show (since they are now registered with the AKC even with all the protests of the breed club)...one lady who works her border collies went up one side of a judge and down the other for putting up a border collie just because it was pretty...unfortunately this is how most dog shows in North America work. The border collie is a breed, now it is a recognized purebred dog...they are in fact a race of dogs as they are from a huge race of simulair dogs....so, a population of natural dogs is called a breed...a dog recognized by a kennel club is called a purebred. Just different breeding practices, there is nothing more pure in a purebred dog than a breed of dogs. It's bascially a little bit of snobbery in humans...since we can no longer discriminate against races of humans we now direct our snobbery towards dogs...when a mongrel may have a longer lineage of natural pure breeding and comes from a direct natural breed....purebreds are more often mixed breeds which are inbred to create a certain look...or a small portion of a natural bred and selectively bred to create a certain color etc.
For true working dogs breeders do not follow the strict rules of the kennel clubs...kennel clubs actually encourage linebreeding and inbreeding especially if you start out with only a few founder dogs. With true working dogs, breeders try to keep their breed as a race and not the tight constant of a purebred...keeping the dog as a race gives the breeder a bigger gene pool and choices. Take for example Alaskan Huskies, the best sled dogs in the world...these dogs are not registered because they are not bred like our purebred dogs. The breeders of Alaskan Huskies use any thing that is fast and there is no set physical standard for the breed except that they are normally long-legged, racy looking dogs. They often have pricked ears and coat coloring of a husky, but those are superficial traits that don't have much to do with running fast. So, basically these dogs are selected for their behavioral conformation...running is a behavior and not physical conformation...they chose dogs with a proper gait...there is no purebred breeding involved in this race of dogs...it's more adaptation involved. Border collies have been used for breeding with this race of Alaskan huskies as well and they still use border collies.
I know I got off topic with the other breeds...but, this will give you an idea. Most people who use a certain group of dogs for a certain activity do not want the strict unhealthy breeding constraints that a kennel club enforces. With the APBT breeders are breeding for sporty dogs, smaller and with enhanced drives...they kennel club versions have the same background except they bred against certain enhanced drives...were the working dog is being bred for behavioral conformation the kennel clubs mainly breed for physical conformation.....and sadly you cannot judge a dog properly by standing and jogging around a show ring...they only way to properly judge true conformation this can only be seen by the dog performing its job.
Any how, I hope this helps you. It's always good to take everyone's ideas and come up with your own thoughts. I have studied this topic of purebreds and natural breeds by reading books by biologist who have been studying and breeding working dogs...
. So therefore my line of thought may be quite different than other peoples...that's OK. You come to your own conclusion.
So, basically the APBT is a direct descendant of a race of dogs...they also used this race to create other bull breeds but by selectively breeding dogs that do not display the enhanced drives to make a more stable pet. The APBT is what I would call a working dog version of the Staffordshire Terriers...The Staff is bred for looks and impact in the show ring, where the APBT is not bred for looks but working ability and the correct behavioral conformation.
