Right lads and ladies, we have a big topic to discuss.
This is a pretty interesting topic and has the potential to be a rather interesting one to talk about.
Old world exodus to the New World: How did we get from the Old World to the New, which Routes, What alternate terrain/oceans are beyond our current map borders? How did Concordia appear and how did we travel from the West side of the world to East without stopping along the way?Pretty big questions there right? Right.
Here is a map of what I think may have occurred.
This is super rough and a terrible representation, im not an artist!The area outside of the old world would be considered a veritable maze of waterways, dead ends, an generally a pain to navigate. As such the route to the Corridor Lands and Concordia's location would be obfuscated by such navigational hazards and hamperings.
Potential Explanation 1: It could be said that the red line shown was found first and brave ocean-faring crews undertook a voyage of incredible fortitude and mapped the outer regions (Which are clearly mountainous from the outside, also not finalised in that mock-up picture). They happened across a vast Delta which led into the broad area, and eventually came across the future Imperial Isle location. This news was transported back and charts were made. The more direct route to Concordia from the Old World was still obscured by the vast array of other channels and routes for now, until a good number of Mercannums later.

There are additional inlets and outlets into the Mercurian Empire, with one being found at the Western End of the Minervan Sea, another South of Pyrencia's Sea of Ashes, and the Sea of Reflection in Gallen via river and coast line. Thoughts?