Before I saw my neurologist a couple of years ago, my B12 level was 270. The doctor gave me a supplement that includes methycobalamin B12, P5P, and 5-MTHF. Since then, I have always tested off the charts for both B12 and folate. The B12 is always over 2000 (I don't even know what the actual number is), and the folate is always over 20 (don't know that number either). The B6 has been high also. The neurologist told me to start taking half the supplement, but that has not changed the numbers. Could this mean I am not absorbing the vitamins even though they are the methylated form? My neuropathy is not any better. I also have one MTHFR gene mutation, the A1298C one. I was also low in ferritin. I have started taking an iron supplement.

If you don't stop the supplement at least a week before testing,
you will show high values. The ranges were made from people not using supplements.

So your testing is showing you are absorbing the ingredients from the intestine well.

There are nutrients in the red cells of the blood too. If these rupture when the sample is taken, they flood the serum and test high. Potassium is another nutrient that does this easily too.
Using a butterfly needle, making the tourniquet too tight will also
burst the cells. Or handling the sample wrong in the lab can do it.
This is called a factitious result.