Galactic Calendaris the in-universe calendar system adopted by the Galactic Senate following the Star Wars Episode IV: A New Hope and the destruction of the first Death Star during the Galactic Civil War. Galactic Standard Calendar is the standard calendar system used to reference all of Star Wars. The game also establishes that Raabat's disappearance occurred twelve years before the events of Fallen Empire, so Fallen Empire must take place in 3632 BBY, and Chapter I-which takes place five years prior to the rest of the expansion-in 3637 BBY. According to the novel The Old Republic: Annihilation, the Treaty of Coruscant collapsed in 3642 BBY, and Star Wars: The Old Republic: Knights of the Fallen Empire states that Choza Raabat disappeared two years before that, or 3644 BBY.
