I dont know if any of your HR told you that NS is considered as 2 years working experience and counted in when they generate package for a males. As such, they usually offer higher package as to female and also because of that, completing a 3 years in public service reward you with the one off merit incentive for 5 years service award.

I have seen many male colleagues who have only 4 years working experience, but because HR counted in that 2 years NS, they ended up getting a package that a female with 10-12 years working experience then can get. This is widely known in public service. If the guys dont believe, they can go ask their female counterparts to verify with their package to see.