Why is it "dissembling" to ignore the second dip in the 1980's, but not dissembling to ignore the second dip in 2002? The NBER declares an "end to the recession" two months after the Atta Boys kill 3,000 people and toss the travel and entertainment business into the toilet, and you'd like us to think that we should expect economic performance to behave the way it always has after the NBER declares an end to a recession. No one knows how 9/11 impacted the economy, or by how much. We can see the effects on travel and tourism, but what were the secondary effects? We can guess (business travel down, trade shows and conferences in the tank, all kinds of stuff) but it would take God to really sort it out.
Whatever the effects were, to assign them a value of zero, as you are doing, is virtually certain to be a fairly large mistake.