When I used 5mg orally every day for 3 months my test was 1999.

Several members here have had results that high when supplementing.

This test shows only the B12 in the serum and not the tissues.
There is B12 in red blood cells too, so if the sample ruptured the cells in the blood that would dump B12 into the serum and be a false (factititious) reading. This happens with potassium tests commonly. Using a butterfly thin needle to draw blood, or too tight a tourniquet can rupture the red cells.

A high reading (and 2000 is often the upper limit of the testing equipment), is not something to worry about generally. If you continue with symptoms over time however, with a high reading, then it would suggest you look for a reason. Adjusting your dosing is the first thing to adjust.

The testing does not discriminate between methyl or hydroxyl forms of B12 and cyano. The test measures the red color of the solution extracted from the serum, and not individual chemical analogues of B12. It is called a colorimetric test.