There was a wholesale re-issue of a new style of card in 1942, keeping the previous numbers. New cards were also issued on a change of name, again keeping the same number. If her number is in the format ABCD:23:4 then it was part of the original registration, and you can use that number to find the person's entry in the original register.
clairec666 - I too have found someone whose change of name was not changed when she married. I have the marriage certificate and I know that she used her new husband's name because her young son from her previous marriage was brought up with his stepfather's surname. I suspect this was because this marriage was in the late 1950s, after registration had ended. You could be prosecuted for failing to notify a change of name or address while registration was in force, but when it was an NHS matter only, it was just another bit of paperwork. So I think most of the un-notified changes of name are post-1952 (although I have a friend who found exactly the opposite in her family!)
