Dan - you may find this extract from another article I wrote on the subject of vitamin B12 deficiency helpful

"Oral vitamin B12 supplements overall have a low absorption rate - 0.5% - 4%. That is why supplements of this vitamin generally tend to be made in very high doses. An oral dose of 1000mcg, which is quite typical, delivers around 5–40mcg of B12. Researchers suggest an oral dose of 50–100mcg daily, or 2,000mcg weekly, for healthy vegetarian adults, taking into account the rate of absorption."