Imagine the scenario: Hundreds of thousands are lying dead in the streets of Boston after a massive anthrax or nerve gas attack. The president immediately calls in the lawyers to determine whether the attacking state is in compliance with the NPT. If it turns out that the attacker is up to date with its latest IAEA inspections, well, it gets immunity from nuclear retaliation. (Our response is then restricted to bullets, bombs and other conventional munitions.)
However, if the lawyers tell the president that the attacking state is NPT-noncompliant, we are free to blow the bastards to nuclear kingdom come.
This is quite insane. It's like saying that if a terrorist deliberately uses his car to mow down a hundred people waiting at a bus stop, the decision as to whether he gets (a) hanged or (b) 100 hours of community service hinges entirely on whether his car had passed emissions inspections.