India doesnt really have S300 just upgraded older Russian SAMs like SA2 with capabilities almost similar to S300. They share same radar and upgraded guidance units. At least this is what is claimed by Indian defense sources. Till this date there has not been a single sighting of S300 inside India.
I mean its been pretty well known that they have had them for quite a while. S-300s aren't exactly rare, the soviets sold them to everyone allied to them.