I don't know very much about conscription, but I can help you with the way the National Register was maintained. The master registers were held nationally, and updated manually. These were the original 1939 Register, and separate registers for people who arrived after the 1939 Register, or were born later, registered late for any reason, or were demobilised from the forces. Each local National Registration Office (NRO) had a card index, compiled initially from the household schedules of the 1939 Register, with new cards created for new births, new arrivals etc. They recorded changes of address within the district, and if someone moved between districts, the new district created a new card for them, and notified the old district who removed their card to a 'Dead File'. The National Register was only notified of the move between districts, not the actual address. Changes of name were recorded in both national and local registers, and when a death was notified the card was also removed to the Dead File and the National Register was notified. Lots of cards, forms and record sheets, lots of people. That's the short version, but I think it covers the gist of it!