Actually I believe the current round play is less that 60,000 rounds annually. Before turning over the club to Noboru Watanabe, the Hathaway family had the play count close to 80,000 rounds one year.
The Hathaways actually opened the door to alternate greens with one at the 16th, designed by Ted Robinson.
There is also one at the 6th.
On weekends all 18 greens are available. During weekdays they open 16 to 17 greens. My last year as a member I played the alternate on #6 2 to 1 over the regular green. Ouch.