@ Mr. Greenwood
there's a "high degree of certainty" because no one in NASA is ever ever allowed to answer anything with certainty. Because if you've taken your math classes, you'd know that there is no such thing as 100% certainty in the real world. Those with sciency backgrounds can tell you there's all sorts of uncertainties Heisenbergian and potentials for atoms to do really weird quantum stuff. Those sick SOB's among you with political and MBA backgrounds know it's all about blame-the one guy who bets his career on a certain outcome, is the guy who will lose it (thanks to the political and MBA types making room for their own ilk)
Not leaving out the zoology guys-understanding the feeding and mating habits of the rabid weasel makes any bureaucratic response (or real scientists forced to deal with them) easier to predict and understand.
But seriously, if the guy were to have absolute certainty that the problem was fixed, the Media and political hacks would destroy him and as much of NASA as they possibly could if anything-even totally unrelated-were to go wrong.