So I'm flying BOS-AMS-DEL-CCU and then CCU-BOM-AMS-BOS. BOS-AMS and AMS-DEL and BOM-AMS and AMS-BOS are all on Delta, where I get to check two bags as a GM. On the way there, I'm flying Jet Airways but will Delta check the bag all the way through to CCU? However on the way back how do it get the two bags? Additionally I would have bought this through Delta, however, I had to buy through Expedia as it was the only way as Skyteam does not service CCU. Any tips?