What should be the Last Name ( Ref Aadhar & PAN - Link )

I-T dept mandate the same name in both Aadhar and PAN. We used to have only initials as last name say

Sunil Gavaskar S ( not Sunil Gavaskar Subramanian )

PAN - name update never accepts one letter as Last Name. Can you people suggest which is right way to re-define our naming pattern.

Kindly note that having father's name or family name in one's last name results in lengtheir names and not feeling good sometimes.

Thanks

Sunil