Danny
Those with a DOB between 1st January 1921 and 31st December 1921 were required to register for National Service on 22nd February 1941.
They would have then followed the procedure that you outlined in your posting 5735.
Also, apologies, but for the purposes of accuracy, I thought it worth pointing out that the National Registration Card was not part of the process of registering for National Service. It was issued during the 1939 census
The 1939 National Identity Card .
The following is an example of the National Service Registration card (NS2).
Regards
Pete