[GameMaster85]

When was the Sigroganian Empire officially established (Presumably with King Erachial in tow) in both current public knowledge and actual fact?

Since it's a dominantly human empire, they could technically have existed prior to the Enlightenment. (when there probably was only humans) But it was more likely they were formed near the Enlightenment. They could have also formed near year 0 as well. (the end of Heaven's Contention) But either way, at least some history was probably recorded past year 0.

(You might also be able to answer the question in repeating with the other major factions as well if you'd like.)