The MCV (mean corpuscular volume) in the CBC bloodwork is elevated when B12 begins to get low.

Dropping so far in a short time, suggests that you are living off the stored B12 in your liver.

The ranges used by doctors are only averages. There will be some people who need more than others, so one person's "normal" would not be "normal" for another, with greater needs.

I really think people who don't feel right taking some vitamins should get the MTHFR DNA test to see if they can activate them properly. If they cannot, the vitamins (B6 is not included) folic acid and B12 will not work, but may show up in the serum anyway in some testing. B6 is excreted in the urine and you can see a slight greenish tinge to show it is coming out. You can't see B12 however the same way.

Pernicious anemia does not affect the white cells in a great way.
Production of red cells, yes. A global decrease in both red and white cells suggests a marrow disorder, or something wrong with the spleen. Seeing a hematologist might be a good idea.

This is a link explaining hematocrit:
http://en.wikipedia.org/wiki/Hematocrit

Some of this is getting beyond my expertise, so consulting a hematologist for explanation might be a good idea.