It does vary from consultant to consultant, the problem with B12 is that your body stores it for a long time, so initial deficiency isn't spotted until a little bit down the line, my consultant requested that I have 3 monthly B12 shots for the first year which I was getting at my GP's, they have an out patients clinic there, so no problem getting my shots!
I've recently had my 1 year post op bloods done again with my GP's and he's taken me of the B12 and Zinc as I’m running slightly high on both, I have another blood test booked up in 6 months where we will again review my vitamin levels!
What I would say is that its far better to have to much B12 stored in your system than not enough, B12 is the most important as deficiency can lead to motor neuron issues and nerve damage longer term!
Having your bloods done initially at 6 months and then 12 months is very important as you need to know if the vits your taking are working or if you need more or less of certain vitamins, in my case I need less, don’t just assume because someone else has been told they don’t need B12 or zinc or even iron that it applies to you, you must follow the direction of your GP or consultant.
Longer term your body will learn to adjust to the malabsorbtion aspects, and you will gain a greater range of vitimins from your diet as it slowly expands, this may result in your GP cutting certain vitimins back slightly, like in my case.