A look at the schedules show that no legacy 77L flights are scheduled post end April. Also I read somewhere that AI is retiring the 3 77Ls pretty soon. 2 are already parked and one is doing del-sfo AI 183 until end april post which ex DL 77L takes over. If the rumor of retiring 77Ls is true then you are good. From DEL, equipment swap can still happen to the legacy 77W but from BOM/BLR you are almost certainly getting the ex DL 77L