Geoffrey,
The topography of the ground and the pretty significant slope down from the 9th green to the current driving range would have certainly helped.
From the original drawing it seems that the 9th green is almost 40 feet higher than the 13th tee.
Today, it's also less of a concern because of trees planted around the left of the 9th green (today's 7th), presumably to protect it back when.
Also, with the army's work on flattening the driving range, you could now run the fairway all the way open to the creek. If someone can post a modern aerial (I can't get Mapquest to cooperate), you'll see what I mean.
I agree...I think further personal investigation is in order.
Another related twist I just noticed is that the 14th hole is listed as 150 yards in 1917, not the 175 conceived in the drawing.
Did they decide to put the green back near the creek anyway? I smell core samples!