Interest on delayed payment of pension

I am a retired Central gov. servant governed by central civil services rules.Date of retirement: 31.3.2010. Payment of Retirement Gratuity and pension was delayed as personal file and service book were lost and not traceable by Deptt..This was an administrative lapse. Orders were issued by the Dept. in 2015 for re-construction of service book . Thereafter pension and gratuity payment orders were issued on 1.2.2016 and were paid on 18.6.2016. I had submitted representation on 16 .8.2016 requesting payment of interest for delay in retiral dues.No rejection letter was received but a reply was received on 5.1.2018 ( thru RTI ) stating that "the claim is old and papers are not available". Thus, it is a deemed rejection of interest payment on delayed retiral dues. Request advice on the following as I want to file a case in Central Administrative Tribunal: 1.Limitation period will count from 31.3.2010 or 1.2.2016 or 16.8.2016 or 5.1.2018 ? 2. Will I have to request for condonation of delay ? 3. Can I claim 12 % interest at GPF rate ( compounded annually ) ? Request advice pl. Ramaswamy E mail ID : [deleted]