Well, I will tell you that you can have complete loss of sensation, I can stick my legs with push pins and into a pot of boiling water but I still get burning and intense pain in my feet and legs. Conversely I would not say that your SFN has advanced because you are no longer getting buzzing or burning. I think the way your symptoms hop around is very atypical which accounts for the lack of response, we mostly speak here from our own experience, others have professional knowledge or wider experience just from years spent helping others on these forums.
I have had numbness in my hips and buttocks, it is an occasional thing, but in my case is part of a clear progression as the permanent numbness is now above my knees and I have symptoms in my thighs. Skin biopsy showed nerves segmented and breaking down at upper thigh four years ago. I also get a very painful constrictive feeling in my rib cage which is only once a week or do but feels like a muscle spasm and responds to Valium. I do not use it regularly but I do when I get these weird things that may be spasms. My wiring is so deteriorated that nothing feels like what it really is.
Hope someone else chimes in, but it s unusual for symptoms to hop around or for arms to be affected rather than hands and feet first.