This is difficult to answer. One of our members who actually began and maintains a website on B12 --rose--- used to post here but has now moved on as she improved with proper treatment.

At one point she was extremely low in B12 and in a wheelchair.
https://sites.google.com/site/roseannster/home

If you search her name, you may find posts from the past that discuss or mention the healing phase of nerves.

I know just from myself, that my PN was terrible in my early 30's, and I had terrible foot pain, which I attributed to my job and long hours standing. (this was 37 yrs ago!). Eventually the pain subsided, and was replaced by numbness, and I became used to that quickly. When my thyroid tests finally showed the hypothyroid state, I was put on levothyroxine, and my feet slowly woke up. The tingling and pain returned, slowly, and then ebbed away. The numbness was gone. This process took a year.

When I joined the internet in the late 90's...I found our previous board for PN and started posting with rose. And now I am still here continuing her work 16 yrs later! Really the medical profession needs to get a grip on this. The American Association of Family Physicians has a wonderful link for doctors about B12 testing and treatment. It was put up in 2003. I have that link on the B12 thread here too. But still daily we have posters joining NT who have never been tested or who are very low and were told they were "normal".

So PN remains poorly addressed by doctors... B12 is only one of many issues they don't track or evaluate for many patients. And PN is extremely common, and aside from the hereditary CMT patients, mostly the causes are environmental.