I think that it may help people longer term to explain that there was/is
* a National Health Number NHS No issued around the years already mentioned
( eg mine MABU 99 )
and
* a National Insurance Number NINo ( eg XX nnnnnn V )
Where nnnnnn is straight numeric sequence number eg 123456 and the quarter of the year ( a/b/c/d ) when issued
Temporary numbers " TN ddmmyy x" where payroll processors were originally told to use
"TN"

date of birth (ddmmyy) plus the single code for sex "M" or "F"
Originally, meant only to be used to go a little way to help identify a person and until issued with a real NINo
NINo is(was), in effect, your account number ( special note = including your State Pension Fund )
with all those implications.
More recent Health Service Numbers have a format of nnn nnn nnnn.