Here is a quote from an article I"ll reference. The whole article is easy to read and fairly non technical: "A serum vitamin B12 level between 200 pg/mL and 900 pg/mL is considered normal, but a threshold of 300 to 350 pg/mL is recognized as a marker for a desirable status in the elderly. The laboratory diagnosis is usually based on low serum vitamin B12 levels or elevated serum methylmalonic acid and homocysteine levels. Elevated homocysteine is an important marker for vitamin B12 and/or folate deficiency. Classic deficiency symptoms such as megaloblastic anemia often fail to appear with subtle deficiencies, as they are usually late clinical signs of severe deficiency.3,4 Symptoms of vitamin B12 deficiency include anemia, neuropathy, and neuropsychiatric disorders."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781043/#:~:text=A%20serum%20vitamin%20B12,methylmalonic%20acid%20and%20homocysteine%20levels.
I would be interested in knowing why Dr. Oaklander wanted your B12 level to be higher than normal. You might ask her to direct you to references that support that idea. Your's is only one case (although it's certainly the most important case to you!), and doesn't prove anything, but notice that even at higher than normal levels, you have noted no improvement, and the disease progression continues. It is possible that B12 has nothing to do with your form of PN.
At this point in time, PN is an extraordinarily difficult and frustrating disease. Hopefully, that will change in the future. This situation affects everyone: patients, doctors, families, etc. Do the best you can, stay informed, and try to have a positive attitude.