Tom,
I think that definition of "green" is something that prompted George Thomas to build his bunker in the middle of the green on #6 at Riviera.
By the 20-yard-circle definition, Thomas correctly pointed out that there were lots of holes that had bunkers within the green. The drawings of the 8th and 11th holes at St. Andrews in his book show that circle with the bunkers inside it.
Anyway, thanks to nregan for printing these numbers. I think Tom is right that Piper was trying to make things a bit too scientific, yet it's instructive to see that there was a wide variety of green size among famous courses even back then. Too bad they didn't collect data from more courses, since the numbers would be of great help in restoring any of the courses they measured.
THE LINKS has a short list of the "championship" yardages of courses in 1926 which is also great to have. I reprinted a few of them near the back of the Anatomy book ... National was 6,163 yards in Thomas' day, Garden City 6,417, Pine Valley 6,446, and Oakmont about the longest at 6,707 yards. Merion was the only course on the list which hadn't added tees.