Being a Payroll Administrator I see many NI Nos. I've noticed that people born in the same year tend to have the same letters at the beginning of their number. For example if I see anyone with a WM number then chances are they were born early 60s. But then again people who arrived in the UK from overseas and were allocated a NINO after their 16th birthday don't seem to follow any pattern I can discern.
However the allocation of initial letters doesn't seem to follow a particular pattern. For example for most of the 1950 births numbers begin with 'Y' and 'W' series begins around 1958 continuing until 1962 when the 'N' series begins. 'N's end in 1973 and then 'J's begin. I can't speak for the sort of numbers they would have been issuing around your grandmother's time but if the "pattern" or lack of it from the 1950s onwards is anything to go by, I doubt you can tell much from the number.
The last letter at the end of the number is either A, B, C or D and used to relate to the quarter of the year, but I don't think this applies any more either!
Heather
