In DTI: Watching The Clock, Commander Juel Duncan traveled back to December 2381, to stop the assassination of Nan Bacco. He even doubled back on her timeline to have the double Bacco help him stop it. What was such a big deal in the following couple of years that Duncan had to come back and fix it if she was meant to die so soon afterward?
My guess would be the formation of the Typhon Pact and ensuring that there would be more of a cold war between the Khitomer Accords powers and the Typhon Pact powers.
More likely the fact that CLB did not know Bacco will be snuffed out soon afterwards when DTI was written.
Which is why cmdr. J Duncan even expressed admiration for Bacco's achievements - none of which, as it turned out, are significant enough to be remembered as exceptional after 600 years