I can recall many years ago meeting a pretty Norwegian girl at an AKC show. She had an AmStaff puppy with her that she had picked up from the breeder at the dog show. She informed me that in Norway APBTs were banned but AmStaffs were still legal. Go figure! When I told her I was a Tosa guy, she asked, "Are Tosas as bad as they say." I said they weren't.
In the fall of 1985, I attended an AmStaff national specialty show held at the beautiful campus of Pepperdine University in Malibu. There was one dog entered who was a red-nose and had yellow eyes. This would have been fine if it had been a UKC APBT show, but a number of the AmStaff people were upset the dog was even there because these things are serious "faults" in the AKC breed standard.
A lot of AmStaff show people would dual register their dogs as APBTs with the UKC to have additional show venues. Some Pit Bull purists were annoyed because the AmStaffs tended to dominate the UKC conformation shows. Turning your AmStaff into a UKC APBT was (and I presume still is) a simple matter of registering your AKC dog with the UKC. However, you cannot register your UKC Pit Bull with the AKC as an AmStaff.
All my knowledge of these matters dates from some years back, so whether these things still hold true, I do not know.