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.
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.