Jim, I've seen early drawings which put the tee much closer to the fifth green, and early on (and during the 1916 Amateur) the par three was the next hole after the present 5th (which was then the 6th.) But those early drawings are pretty rough, so I couldn't say for certain whether there used to be a tee even closer to the 5th green than the two still existing small tees.
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Sean, I think CBM just viewed these things much less stringently than you do. He not only called Merion's hole a reversed Redan, he also wrote that the Redan "principle can be used with an infinite number of variations on any course." That doesn't jibe with your strict understanding.
If you think about it, from a purists perspective the very concept of a reversed Redan is somewhat absurd anyway because reversed Redans don't play anything like Redans for the vast majority of golfers. But CBM was willing design and build them and all sorts of twists, like the reversed Redan at Sleepy Hollow where the green was well below the tee. I am not sure if many of CBM's Redans would qualify as Redans by your standards.
As for why Merion looked so different than other CBM course, I have never seen any indication that CBM/HJ Whigham/ or Raynor were directly involved in the actual construction at Merion East. So far as I can tell, Wilson was the one responsible for constructing the course. CBM's contribution was in the planning, but Wilson is primarily responsible for how that plan was carried out. This is why I don't think I have ever argued that CBM was the "main archie" for the creation of the course. I have said he was most likely the person most responsible for the plan, but that it was Hugh Wilson and friends who actually built the course. No doubt it would have turned out differently if CBM and/or Raynor had been in charge of the construction. That said, some of the earliest photos of NGLA don't look like what many think of as CBM's work either.
As for the "main thrust of evidence" of CBM's involvement, it comes from Merion's own records and the recollections of those involved. Among other things, he inspected the property, helped choose the land, worked with Wilson to create the layout plan, again went over the land, and even chose and approved the final layout plan! What more evidence could you possibly need that he was significantly involved in the planning?
As for whether CBM ever saw the hole, I can't prove one way or another, but he seemed to think it was a Redan Hole and he listed it right there with his other Redan holes in his article on the Redan. Regardless, many other experts including those who had seen the original said the same thing. The hole was widely known as a Redan.
Isn't it possible they just viewed things differently then, than you do now?