I think I have found the rule. Please refer to Schedule II, Section A,
8 (d) of the Aircraft Rules 1937 which states that-
(f) An aircraft type to be included in the Aircraft Rating of a Pilot’s licence shall be the aircraft type on the Indian Register of Civil Aircraft and in respect of which a valid Certificate of Airworthiness is in force.
Hope this helps. I was told by one of the DGCA official to write the DGCA regulation exam again to find the answer to this question. Good that I managed to get it without writing those exams again.
