We know Dalmasca has been around for a thousand years already. Ivalice is even older then Dalmasca is. So old Rabanaster was built on top of the Ivalician capital and none of the Dalmascan's ever found out about it.

In addition, Ramza and Delita's story is about the start of Ivalice's Golden Age. So there's probably a rather large gap between Ivalice and the start of Dalmasca. I'd say Ivalice (and probably Goug) would have to have been in the 5th Astral Era at the earliest.