So data point at DEL. Ticketed ATL-IST-DEL-DED with boarding passes, and a very tight connection between T3 and T2 at DEL, the guard at T2 would not let us in with a boarding pass and passport in hand. We had to spend 20m at the landside Indigo counter for them to print out the iternary with the bar codes and then he let us in--just in time for our flight to be closed. No where did TK or Indigo let us know we needed to bring anything to get in T2 at our I-D connection.