George says so.
A little less tongue in cheek...when something like the Essential Chronology is approved by LucasArts to say Revan was LSM and Exile was LSF, that essentially means it's received the 'blessing' of LA to set the genders and lightside/darkside of that particular character. Practically speaking, whenever _you_ play the game, you can make him/her whatever gender and light/darkness you want. They only set a particular canon/lightside/darkside orientation for purposes of publishing stories, comics, and so forth down the road so that there's some continuity. It would be very confusing if there was a LSM Revan in one novel, but a DSF Revan in a comic book series. LA sets the genders and other details so that that type of confusion doesn't occur.