Tom,
I believe you are correct across multiple fronts.
The more the architect had a chance to word during a certain period, the more opportunities they had for a project to be ranked in the top 100. Both from familiarity and from their style being in vogue during that period. Keeping in mind these are subjective rankings and the whim of the raters plays a large part of this.
It would make sense that internally these rankings don't want to over-saturate an architect and when they hit a particular threshold they begin to rate that architects work against themselves. In 1979 the only Dye course ranked was Harbour Town, over the next 10 years his participation in the rankings grew to include 8 courses. When the Ocean Course was added in 1991, PGA West was dropped, keeping his course total to 8. When Whistling Straits was added in 1999, Long Cove was dropped, at that point Dye was holding at 6 courses in the top 100.
Interesting point for RTJ. He never had a new course added to the list. his newest course to be ranked was Valderama, built in 1975. The only two architects to have courses built prior to 1979, and after 1979, in the rankings are Nicklaus (2) and Dye (5).
Of the "modern" architects in the Rankings:
- C&C: 4 currently ranked, 7 total ranked, 7 built in a 20 year period
- Hanse: 4 currently ranked, 4 total ranked, 4 built in a 22 year period
- Doak: 7 currently ranked, 8 total ranked, 8 built in a 20 year period
- Fazio: 0 currently ranked, 9 total ranked, 8 built in a 17 year period
All of Fazio's designs have been dropped from the top 100 and half of C&C's ranked designs have been dropped. So it will be interesting to see what happens next. Will C&C continue to add courses to the list, replace current courses, or begin to slip farther away?