I don't know if it is possible to give a conclusive answer to your question though a drop of that amount would seem to suggest that there might be an absorption problem even though the time period is over 2 years.
Bit confused though as looking back in your posts the seem to imply that you were self injecting methyl a year ago, as do some responses from a month ago - is this correct? or does the question relate to someone else's results?
Whilst someone with a severe deficiency from dietary sources might be given B12 loading shots to get levels up again it's pretty unusual - though it isn't unusual for GPs to assume that a deficiency is due to diet even though there is no real evidence to support this because there is so much fixation on IFA testing and action on potentially inaccurate results leading to an assumption that PA isn't a problem ... compounded with an assumption that PA is the only absorption problem.
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