According to British Society for Haematology (BSH) guidelines and NICE Clinical Knowledge Summaries (CKS), the primary beneficiaries include: Key patient groups who may require B12 injections include: Pernicious anaemia patients requiring lifelong hydroxocobalamin 1mg intramuscularly every 23 months following initial loading doses Patients with gastrointestinal disorders including those who have undergone gastrectomy or ileal resection, and patients with conditions affecting B12 absorption such as Crohn's disease or coeliac disease Strict vegans and vegetarians though oral supplementation is usually sufficient unless malabsorption is present Elderly patients who may have reduced gastric acid production affecting B12 absorption Patients taking certain medications including metformin (MHRA advises monitoring B12 levels in long-term users, particularly those with risk factors or symptoms), proton pump inhibitors, and H2-receptor antagonists long-term [6] Individuals with neurological symptoms such as paraesthesia, ataxia, or cognitive impairment related to B12 deficiency Pregnant women with confirmed deficiency (hydroxocobalamin for malabsorption

B-5 is the anti-stress vitamin due to its vital role in the formation of various adrenal hormones & steroids, & contributes to the production of important neurotransmitters in the brain
Further, NICE and the BNF says that if there are neurological symptoms present, then every other day injections are the recommended treatment, so all the points you make about B12 being stored and sufficient are not really relevant
The commonly used method is high-performance liquid chromatography, supplemented by other validation methods, as detailed below
Description 5-Amino-1MQ is a small-molecule research compound used in controlled in-vitro studies of nicotinamide N-methyltransferase (NNMT) activity, NAD+-linked metabolism, and cellular pathway signalling under non-clinical laboratory conditions
These are research figures, framed for research use only