I think you are mixing up milligrams (mg) with micrograms (mcg)

B12 orally is not well absorbed. It has to be taken on an empty stomach, for passive absorption at all.

1mg =1000mcg. In a one milligram (1000mcg) dose orally there is a study showing absorption of 13 mcgs.

The FDA has not set an upper limit to B12 ingestion, because in all the years it has been researched NO toxicity has been demonstrated.

The amount of B12 in food is normally 1-2mcg ....and the way it is absorbed, it must be in stomach acid for the special carrier in the stomach called intrinsic factor, to work, and carry the tiny micrograms thru to the intestine where they are absorbed and carried off by transcobalamin.

Many people have this delicate system broken and therefore oral tablets are quite high seemingly, but in reality very little is actually absorbed.

This is my B12 thread, and it includes the link to NIH you read.
But you need to read more slowly and carefully, and perhaps more than once to understand it all. This is why doctors don't "get it" as well.

http://neurotalk.psychcentral.com/thread85103.html

B12 is essential for maintenance and repair of the nervous system. Any tiny error in its absorption and transport, and you will suffer. Low acid in the stomach is one common cause, because people take the OTC acid blocking drugs too much. New estimates are that about 40% of people are therefore low in B12 today.
In the link I gave you above, in the first post, is a video on YouTube... I suggest you watch it first of all.