this is definitely conjecture but Have you noticed the Geography of which characters have what Crests? The Empire is pretty much loaded with 4 Saint Crests. Indech, Cichol, Cethleann, Mariul. Meanwhile the Alliance and Kingdom have 10 Elite crests. There is a support with one of the Blue Lions (Pretty sure it's Sylvain.) where he says having a Crest is important to defend the land from monsters. It keeps it liveable. Maybe Serios sent the 10 elites and their bloodlines there to expand the reach of Fodlan. Because it likely wasn't as liveable as the southern region which is stated to have good granaries and is easily defensible from invasion. The Northeast part of Fodlan has monsters and Almyrian attacks. So they sent a lot of the 10(11) elites there. Rewriting the history of it to cover it up doesn't seem too farfetched.