cmc64 has it straight...except that they didn't have either the vocal or piano cluster at the 3/23/74 "Sound Test", and both instead used individual low-driver cabinets arranged along a curved path. The hi-driver clusters appear to be completed for both vocals and piano at this time. The vocal cluster debuted at Reno on 5/12/74, the first road gig for the WOS. There seem to be almost NO pics available from June tour (!) but the piano cluster finally shows up in Jim Anderson's shots from July.The February 22-24 1974 Winterland was set up very similar to 3/23/74.
Count all the shows from 11/30/73 to 10/20/74 and you've got your number... but for my money, I would extend it back to the aforementioned 2/9/73, since it's essentially the same system, including the out-of-phase mic pairs.
"There, in huge black letters, was 'The Grateful Dead'. It just... cancelled my mind out."-Garcia