--it depends on the spine issue; some mechanical issues, such as a bulging disc, can be reabsorbed/heal over time, and a disc bulge on an earlier MRI may not show on a later one. This has happened to me at the C3/C4 level (and I did question it, given that I had earlier films and reports). Problems with bone spurs (osteophytes) that cause foraminal narrowing are much less likely to resolve

That said, B12 deficiency can cause a very wide range of symptoms/problems, especially if levels are low for a very long time (and I bet your were). Not only may there be anemia, not only may there be peripheral neuropathy, but ther may be subacute combined degeneration, in which nerve in the spinal cord are demyelinated and damaged. There are even people with long-standing B12 deficiency who look like they have MS lesions on brain and spinal scans--one reason B12 deficiency is supposed to be checked any time there are neurological symptoms and unusual MRI readings in those areas.