1974 marked a milestone for vintage timex watches. You will notice from this point onwards an extra digit was often added to the model reference and movements numbered under m100 had a zero appended before them i.e. 2474 became 02474 (M24 movement 1974 production). I suspect this was because the model range was expanding requiring more codes that the previous formula would accommodate. That and preparations for the M1xx movements which were launched later in the 1970s.