Revalidation of duty credit scrips limited; re-credit of special additional duty allowed only under custody or short validity conditions. Amendments permit revalidation of freely transferable Authorisation and Duty credit scrips only when validity expired in Customs/RA custody; introduce a six month maximum revalidation from endorsement to allow re-credit of 4% Special Additional Duty into freely transferable Duty credit scrips (including DEPB) where remaining validity is under six months; establish 24 month validity for Chapter 3 duty credit scrips and restrict DEPB revalidation except under those two exceptions.