Who decided those are SW VA rifles? And why?
Wallace Gusler, on the basis of the triggerguard design and the tang screw treatment, among others things. The triggerguard proportions show up in later rifles from that region and nowhere else that I am aware of, and the use of a woodscrew to secure the barrel tang is a southern thing later on as well. There are some other details too, but I forget what they are - you will have to talk to him. Gusler attributes them to Hans Jacob Honaker, which I am a little less convinced of, but seems like a reasonable guess to me. We know it was done by a European-trained gunstocker with a limited toolset and a background in folk rather than formal European carving designs, and a Swiss immigrant who did his indentures working as a joiner and took up gunmaking as soon as he was free fits the bill. If we could be certain that he was trained as a gunstocker in Europe, which would explain he switched trades once his indentures were paid off, then he'd fit perfectly, but as far as I know that is still supposition.
Gusler gets a lot of grief for attributing everything to Virginia, but I think he makes a pretty good case here. It is certainly a better case than any other I've heard yet.