Teeth of the Tiger puts a big emphasis on being "post 9/11." This doesn't make sense to me because WAY WORSE THINGS HAVE ALREADY HAPPENED IN UNIVERSE! Denver was NUKED! It was so bad that they got rid of ICBM's. Why does 9/11 get attention in light of this?
This can be easily explained. Clancy has often gone on record with the fact his books are an allegory to the time they were written, and if given a choice between canon consistency and getting his point across, he often chooses the latter, though it doesn't diminish the validity of the argument 9/11 would be far less horrifying than the nuking of Denver or worse, the biological terrorism Daryaei used in Executive Orders, which does get referenced in TOTT.
I noticed the same problem in Rainbow Six. There's a bit where a character scoffs at someone saying that now that the Cold War is over the world is a more peaceful place. This is a bit of our universe bleeding into their universe. In our reality this was true, but in their reality there were a couple extra wars that happened in the 90s in Deb of Honor and The Bear and the Dragon.