A past post re a doctor who had unknown B12 deficiency, despite being a doctor and working in a hospital - not one doctor/specialist knew what was wrong with him. As well as others with deficiency. cursor along to about 21 mins in to read about the doctor in particular.
youtube.com/watch?v=BvEizyp...
Dr Chandy lost his licence because he prescribed lots of B12 to patients. It was also reinstated because he, like Dr Skinner, kept meticulous files on his patients.