Check out the 1973 schedule. Even if the concerts were sold out, you could hang out on the lawns outside and hear everything because it was an open air venue
Notice they had a TV show mystery concert. They would broadcast that show on primetime a few nights later. You had no idea what bands would play but you knew it would be top-notch for television.
For 1973 it wound up being Sly and the Family Stone
The Mahavishnu Orchestra sets were released as Between Nothingness and Eternity.