Chris
As I said before I don't use the term as it relates to golf architecture because it is too confusing. Any term that is also used to describe Greek and Roman aesthetics is not useful in describing the works of those talented golf architects of the first decades of the 20th C.
And no one agrees. One poster's definition is the 1920's. You said it could be used to describe some of Pete Dye's early courses. Another says it means strategic. Another says it is older indicative of a particular style popular between 1900 and 1940.
Is the term used to describe a sylistic movement: Greek and Roman aesthetics: ballanced, symetrical, formal, restrained, regular, simple.
Is the term used to describe golf courses "of the highest rank; being a model of its kind", for example: Cypress Point is a classic example of 1920's naturalistic design or Pine Tree is a classic example of post WWII architecture or Harbour Town is a classic example of post-RTJ architecture.
Is the term used to describe a golf course that is famous or well known, especially being traditional or typical. not very illustrative unless it is matched with a more descriptive aesthetic style or strategic style or age/era/movement
The use of the term when describing literature or automobiles or music or many other art forms is usually enduring. You take the use of the word enduring too literally. The designs, design methods and design theories of Donald Ross are enduring even if his golf courses aren't all presented in mint condition. The big picture. Or you can go the opposite directions, perhaps a single hole endures or green or bunker or a strategy. Very small surviving features can illustrate a certain classic type.