What Exactly Did NORAD Learn When They Ran Live-Fly Hijacking Exercises Before 9/11?

Several articles came out in the mainstream media in 2004 that described how before 9/11, NORAD ran several exercises with real aircraft that were posing as hijacked commercial airplanes. In at least one of these exercises, there was a simulation of a hijacked plane crashing into a building. Other exercises did not involve real aircraft but merely involved simulating an airplane crashing into a major building, such as the Pentagon.

These articles are summarized nicely and discussed extensively in chapter 19 of "Crossing the Rubicon".

CLEARLY the US military was aware of the threat hijacked airplanes posed as weapons in the hands of terrorists.

The question is-- what exactly did NORAD learn from these exercises? Did they learn that their jet scramble response was not good enough to intercept the hijacked airplanes-- or that it WAS good enough to intercept the hijacked airplanes?

If the former, what did they do about it?

If the latter, what happened on 9/11/01?