This isn't the first time they've lost something important.
I read a while back that they can't seem to find the blueprints for the Saturn V rocket.
From Popular Mechanics, April 15, 2003:
In addition to propelling America on the most dramatic voyages in human history, the Saturn V created a curious urban legend. In 1996, John Lewis, in his book Mining The Sky, made the startling claim that NASA had lost the Saturn blueprints. Like all rumors, the story contained a grain of truth. Paul Shawcross of NASA's Office of Inspector General came to the rescue. While the claim that the blueprints could not be found was true, that did not mean the engineering genius of the Saturn had been lost. The plans for the world's largest rocket still exist, on tiny pieces of microfilm.
And from the alt.folklore.urban newsgroup:
WHAT HAPPENED TO THE SATURN V PLANS
Despite a widespread belief to the contrary, the Saturn V blueprints have not been lost. They are kept at Marshall Space Flight Center on microfilm.
The problem in re-creating the Saturn V is not finding the drawings, it is finding vendors who can supply mid-1960's vintage hardware (like guidance system components), and the fact that the launch pads and VAB have been converted to Space Shuttle use, so you have no place to launch from.
By the time you redesign to accommodate available hardware and re-modify the launch pads, you may as well have started from scratch with a clean sheet design.