This is what I know, or at least think I knew before, and now afterward of trying to read maybe one page total of this thread:
Hugh Wilson, the much beloved and devoted SPORTSMAN--whose ghostly spirit I once saw gleaming down upon me from the upstairs railing of the vacated, closed-on-Monday, Merion locker room (while trying to collect my senses, recovering from heat-prostration after experiencing a 102 degree/98% humidity, charming Philadelphia day.) stopped into Southampton for a visit with C.B. MacDonald, and conversed with him on what to look for/how to study golf architecture on his way to see the Great Links of Great Britain.
Wilson came back and took those principles--which he learned from that meeting and what he saw abroad, found them in the ground on a somewhat convoluted parcel and built one of the great courses in the young American SPORT. They had trouble getting playable turf grass to grow, and after some consultation from C.B. MacDonald, H. Whigham and many other well-respected experts, who played a Sport that required the ball to utilize slopes, contours and other natural aspects of land to get the ball into the hole, finally did get it figured out.
The course that Wilson laid out, along with his brother Alan, William Flynn, Joe Valentine and many other passionate people, many of them Italian laborers--or in this case artisans--evolved over a period of time and is still a defining attribute to the sport today and has contributed to some of American Golf's Greatest Moments in History. The course has perfected itself over time. (Well sort of)
It's that simple.
There are no missing puzzle pieces. Just the hope of finding pieces of paper or photographs that say who did what and what they were thinking--IF that evidence even ever existed.
Enjoy Merion. I don't think a golf course has ever been more passionately discussed on this website. THAT has to mean something. I know this from experience.