Testing is not a perfect science. Things happen in testing...calibrations can get off, etc. So tests are only snapshots in time, and with a repeat, say in 3 months, you should know more. I'd ask for an MMA test also at that time. If your MMA is low that indicates B12 is working for you.
As far as labs go... Quest admitted to using wrong calibrations for a YEAR in testing Vit D levels. All their tests for everyone were in error for a whole YEAR. So one cannot rely on tests 100% for anything IMO.

B12 is stored in the liver. So some of it may be going there to make up lost stores. It is also transferred into the CSF...cerebralspinal fluid to go around the spinal cord and into the brain. Blood work is for serum, only and does not reflect what is happening in the tissues of the body. Only what is floating around at that time "loose".

You are not back to where you were...and that is the good part.

As your body, gobbles up the B12, there are bound to be temp changes in blood level. If this concerns you alot...take an extra one 3 times a week, at 2 a day... and see if that changes things.