PN symptoms are a common complaint after surgeries. Any type of spinal surgey in any area of the spine, cervical or other, can be an issue to consider on the onset of PN.
Your first B12 of high 300's was not high 'normal'. That figure is over 20 years out of date. As far as Rose's research goes, anything under 600 is suspect. The post shot B12 readng, in the 1300's, is what would be expected. I've been taking oral methylcobalamin (1000mcg/day) for years and my B12 regularly reads in the low 1200's. (The doc notes that I suppliment B12 on the test sheets)
My neuro ordered the skin punch biopsy on the 2nd visit to confirm his Dx of small fiber PN. It did. The Sural biopsy is for other types of PN, and rarely does anything other than confirm the Dx, but can have long lasting negative side effects. The skin punch does not have any long lasting s/e, just 3 band-aids and 2 wks of healing. No scarring to mention of.