Thanks for the info, Beach Man - I live in Britain though, and all the brands mentioned here are American! My preferred brand is Lamberts, which is the methyl version, which has worked for years. I only bought this other one, Nutriseed, because Lamberts did not sell theirs for a while. And I suspect that Nutriseed, which does not seem to have worked, is cyanocobalamin. Have tried to find out, but unfortunately these days they are always "experiencing a high volume of calls" .....
I've got some new Lamberts' just now, taking them daily, and I hope they will do the trick. Unfortunately, a B12 deficit does not right itself easily, if at all.