From Emmet's review of the Piping Rock Biarritz, which--correct me if I'm wrong--was the first CBMetc. Biarritz:
"There is a hog's-back extending to within thirty yards of the green and a dip between the hog's back and the green. Under normal conditions the hole has to be played with what is now known as a push-shot, a low ball with plenty of run which will land short of the dip and run through it onto the green." My emphasis... the ball hits pre-swale, pre-green, rolls through the swale and onto the green. One green.
The Dunn hole did not have a double-green.
According to accounts of the Biarritz holes at St. Louis, Lido, Creek, Deepdale, Shinnecock, Gibson Island, Fishers Island, etc. the Biarritz holes on these courses did not possess a double-green.
In his book, George notes Yale and the Links as possibly being exceptions to the single-green design. (Maybe George can let us know why this is true.) Would it have anything to do with the water hazard, which was the first one to appear on this type of hole? (Again, correct me if I'm wrong.)
Why would RaynorBanks/Banks change the design of the hole later on and go to a double-green at Knoll West, for instance? Why would Hackensack or Forsgate differ from the original design?