McDougall's newsletter (http://drmcdougall.com/misc/2007nl/nov/b12.htm
) does state something about Nori seaweed having the vitamin, but he also says:
“However, there is still some uncertainty about nori as a reliable B12 source; therefore, I suggest if you do choose this seaweed that you should monitor your B12 levels by blood tests now, and if adequate, every 3 years.”
Notice, McDougall is not strongly recommending that anyone take Nori as a source of B12 at this time. And, please remember, McDougall is not God, but he does provide an educated opinion. Just because you may have benefited from his diet does not mean that he is correct in all matters—you are responsible for your own health choices. In addition to that, consider the current concerns of some people regarding the Japan nuclear accident and seaweed radioactivity—now you would be investigating B12 and radioactivity.
My current understanding of McDougall's approach is to treat the body as a complex system that we don't really understand well. This means that we don't unbalance the system by shoving large amounts of specific nutrients, such as vitamin A, D, etc. This philosophy is validated by studies showing that shoving large amounts of something into the body can cause cancer, or other problems. My own primary care physician believes this philosophy as well.
Also consider the fact that McDougall still has partial paralysis from his stroke at the age of 18. (http://www.drmcdougall.com/misc/2009nl/apr/why.htm
). A man with that sort of problem may have difficulty thinking that an easily solvable problem such as B12 deficiency could be worse than the alternative of eating meat and eventually facing a heart attack or stroke. Dr. McDougall is doing a lot for the prevention of heart attacks, but don't forget that he is still a man and has opinions.
VeganHealth.org gives a nice comprehensive overview of this vitamin and the health of vegans. (http://www.veganhealth.org/articles/everyvegan
). They explain a lot about B12 that I have not seen so well described elsewhere.
Videos about B12 from McDougall and a guy who talks about the different types available. (http://lycopene.newaini.com/2012/07/26/ ... tamin-b12/