Great explanation Vimanav!
The one thing I'd add is that the one restriction for Winter Open Skies has to dw with new services. For example, BA
curently operate from LHR
to BOM, MAA, DEL and CCU. They're free to add as many frequencies on these 4 routes as they wish, so long as the slots are available. They can't, however, add an LHR
-AMD service unser this policy. Also, an airline that does not already serve an India route can't simply start flying just for the winter.