The thing most of you guys should probably come to realize and accept is most architects, and certianly architects in Macdonald, Tillinghast and Flynn's day used features (massive bunkering and such for instance) as concepts in what they did. The generally got that concept from somewhere and simply because the feature in that concept did not look exactly like in dimension or something else the feature they took that concept from does not mean they didn't take the idea from it.
We know for a fact that the 2nd hole at NGLA was modeled after the sahara concept at Sandwich because Macdonald and Whigam wrote a rather long article about NGLA's #2 hole explaining exactly that.
It seems pretty obvious that Tillinghast is given credit by Crump and most everyone else for the idea of HHA on the 7th at PVGC. There may be something somewhere in Tillinghast's voluminous writing where he explains exactly where he came up with the idea of a HHA which he referred to in "The Course Beautiful" as "the great hazard" as being the prime factor in a sketch he drew of the true "three shotter", a par 5 that no one was supposed to reach, in concept, in two shots.
Seeing as Tillinghast was an early writer and very good player he undoubtedly was aware of NGLA as practically every good east coast architect and good player of that early time was. (Macdonald was a friend of Crump's, and probably Tillinghast's too, and he did make at least one early visit and another later visit to the site of PVGC (at first he called it "Crump's Folly" and said it could be a great golf course if Crump could figure out how to get grass to grow there---which coincidentally became a huge problem just as it had at early NGLA!).
So it's probably very appropriate to assume that HHA was a loose "concept" use of the sahara concept from Sandwich and then NGLA in a different arrangement. This is probably not much different from the "concepts" Macdonald noted and drew in Europe for his NGLA. Many seemed to think Macdonald exactly copied many of those holes in Eurorpe. By his own admission (and writing) he did not---or not entirely. What he did is encorporate some of those "concepts" of entire holes or parts of them from Europe into some of what he did at NGLA. Probably half the holes of NGLA are that way and the other half are completely original holes. Tilllinghast was logically no different. He was certainly familiar with European golf and architecture having spent time there before and in the beginning of his career. It may be true to say that Tillinghast originally came up with the idea of what he called "a great hazard" smack dab in the middle of a super long par 5 for that time. It's known, also that Crump even before he began building PVGC wanted two par 5s that were impossible to reach in two shots so with that requirment and with the application of Tillinghast's "great hazard" of 100 yards long (Tillinghast actually said that) the idea of the true "three shotter" of the type of PVGC's HHA #7 was born. But the very idea of that enormous sand hazard probably came from somewhere and most like NGLA by way of Sandwich.
As said on this or another thread there's no quesition at all in our minds that William Flynn borrowed the concept of PVGC's #7 HHA in his later designs, probabaly exclusively his long par 5 designs.
Again, Flynn was extremely familiar with PVGC---he was actually lent by Merion to finish the construction on holes 12-15 and to solve the agronomy problems on the course following Crump's unexpected death. Flynn was a member of PVGC as was his partner Howard Toomey.