Ted,
The moment you insert the word "pure", you present the question in a context such that it can't be answered.
Primarily because it's probably impossible to determine what ROSS actually designed and left on site when he walked away from the project.
Absent knowing what existed on the day that Ross completed his work, you can't state what's "pure" Ross versus what's adulterated Ross.
Ross's crews, green superintendents, green committees, boards, Presidents, pros and mother nature could have altered his work and few if any would know about it.
But, to address your question, I think you have to divide and conquer.
The first and most significant element of the question is:
The routing.
Next is the green complexes, followed by a variety of features including bunkering, creeks, mounds, etc., etc..
Lastly, and I wouldn't include this as a category is the tees.
I think the principle of elasticity, a principle that the architect incorporated into the original design, automatically negates the theory of "pure"
While I tend to gravitate toward "pure", I've come to accept "sympathetic", where "pure" can't be achieved, for a variety of reasons.
What's interesting, in the context of your question, is how existing golf courses, where the architects are still alive and well, aren't "pure"
I'd say that very few golf courses that have the luxury of having the original architect available for consultation, are the same as they were on opening day, or from what the original architect intended.
One must never forget, although, TEPaul does it every time, that the nature of memberships is to alter golf courses.
Prospective members are attacted to a golf course, and join it, and the first thing they want to do is to change it.
Why did they join in the first place ? Didn't they like the golf course just the way it was ?
The critical responsibility of any member, green committee or board member, is to protect the architectural integrity of the golf course, and not to alter it to satisfy their personal agenda or the latest fad.