Clancy said that he was able to construct his scenarios from publicly available information, and the rest was conjecture. His accuracy made many uncomfortable, but they should really have been thinking that our enemies could have drawn the same conclusions.
When asked what would he would do if he were given classified information, Clancy said he would call the FBI.
You are absolutely correct in that...
He was eventually given access to some information to give him the ability to clarify, and make more accurate the “outcome” of certain story plots...Not exactly divulging clasified capabilities or procedures, but he was one of the few literary folks to be trusted to NOT give away too much that would jeopardize our armed forces...
That is why a lot of us in Operations, and other tactical jobs appreciated the “edge” he put into his writings...We could relate to the folks he put into those stories, and the situations they were placed in...So in the end it all worked out, and most of all...
We were aways entertained...
I'm sure that our intelligence community knows our enemies can draw accurate conclusions, they just don't want a well-known author to put those conclusions in print!
Heck, for all we know, Clancy may have worked with the NSA to spread misinformation through his novels...