Paul,
Sadly, the NGF is notorious for this kind of reporting. They have categories of "open for play", "under construction", "renovations" and "In Planning." They aren't too picky about distinguishing the nine holes from the 18 hole courses either, so if you took all five categories, they might total over 1000.
However, they get reports from gca's like me, and some of us over report to make our portfolio look better. And, NGF doesn't have the field staff to go out and verify other than the fax response they get.
I recall one gca who kept a listing of a 3 Hole remodel project in Omaha on the list for over a dozen years after completion so, presumably, he could see his name on the list when times were lean. On the other hand, I tend not to respond to those lists, since I don't want a bunch of phone calls. It may even out, but I bet there is more over reporting than the other way around.
I think the actual number of new cousres is closer to (and probably below) the 150 already stated, with about 150 also closing. Last year was the first year in a long time there was no net gain of golf courses. In the lean, high gas price era of the 70's there were still about 150 courses built in the US of A, so that number makes sense to me. Every time I think "no one is building courses" I recall that it is a very huge country, and there is no national economy, just several regional ones, driven mostly by housing. So, 150 is possible, even if nothing is going on in your neck of the woods.
Heck, even a gca "doomed to mediocrity" (who shall remain nameless for this discussion.....) has two 18 holes in planning, two nine holes and two full reconstruction master plans, so someone must be doing something.