I have a great story about the Knoll hole.
One of the best friends I made in my year in the UK after college was a fellow named Dave Oswald, who was the art editor for GOLF WORLD (UK) at the time. In 1986, the magazine sent him over to the US to cover the Open at Shinnecock, and I met him on the Sunday and we played National the next morning and then I took him to Piping Rock to show him all the stuff I had been working on for Mr. Dye there.
When we got around to the 13th at Piping Rock [the Knoll hole], he said, "I know exactly where Macdonald got the idea for this hole. It's the fourth hole at Scotscraig, where I grew up." I asked him what were the similarities, and he said that on top of the pitch to a small raised green, the green at Scotscraig had two tiers [though not as severe a slope as at Piping Rock] and it had to be what he was thinking of. I was surprised at that, because Macdonald was always pretty forthcoming in naming the holes he admired from the UK in his writings, but he never mentioned Scotscraig in print that I'm aware.
George and I stopped in Scotscraig to see the hole 3-4 years ago now, when we did our little tour of Scotland. Absolutely no doubt in my mind that's where Macdonald got the idea. Now I have to wonder what other ideas he failed to attribute ... the 17th at Lundin Links as the model for the 16th at National is the only one I've found so far.