It is easy to miss, because it is in a sidebar at the very beginning, but it is spelled out explicitly that the date for the beginning of the game, used as the standard of reference in the encyclopedia, is 3640 BBY, thirteen years after the Treaty of Coruscant.
Interesting. I went through the Journal of Gnost-Dural yesterday to get the actual years for the cinematics leading up to the game. There's a 13-year span between each event. Thirteen years before the game was the Sacking of Coruscant. Thirteen years before that was the Battle of Alderaan. Thirteen years before that was the arrival of the Sith at Korriban. The writers seem to like that number for some reason.