"Ancient" Earth culture and history...

[teschy]

Could be more than 3017 A.D. We do not know how long the journey to the Sirius sector took.

As for the recorded history ? Well, who knows. In 800 years, a lot of stuff can happen, records can be lost or deliberately destroyed by certain groups (look at the Hispania for example). It's hard to tell, probably some of it was preserved, but surely some of the history is either taboo or hidden from the public.