No time limit prescribed in law for amendment of shipping bill: Expert

The only condition is that the document on the basis of which amendment is sought should be available at the time of export

We made shipments in January 2018 to June 2018 under advance authorization and now came to know that inputs mentioned in the advance authorization can be imported duty free under Free Trade Agreements.  We want to convert our above shipping bills from advance authorisation to drawback shipping bills, as per Para 4.49 (e) of Handbook of Procedures, Vol 1, where no time limit for conversion is mentioned. However, the relevant custom circular for conversion of shipping bill 36/2010-customs dated 23rd September 2010 says that request for conversion must be made within 90 days. Considering the fact that our shipping bills