Yes depending on the bloodlines he could have himself an American Bully, American Bully mix, Amstaff mix, APBT
mix, Pitterstaff...or any mix really! Scatterbred....to create the American Bully other breeds were crossed in. They were not created simply using AmStaffs/APBTs
But typically if he is still only ADBA and not even UKC a lot of paper hanging has been going on most likely.
Not even sure what your question is.... Because people began just breeding and cross breeding and hanging papers that is why you could have a total mutt be registered. That is why it's important to trust your breeder, and the breeder before him, yada yada...
The bloodlines tell you what breed or mix of breeds you have , at least on paper.