[@Paradoxial] Looks interesting, here's somethings I'd like to point out.

You have a lot of titles, the ones that are listed in the House CS aren't the ones also personally assigned to the Head of the House/individuals. I don't know what each one exactly means but I imagine that Slayer of the White Bear is more a personal achievement. You'd also definitely have "Lord of Appalachia" as one of your titles since that would be a crown given one to signify your rank and ownership of the territory. I do like the idea that you have some titles that implies a sort of disconnect/isolation from the rest of the Five Kingdoms (Mountain Mother and the Digger ones especially).

The Five Kingdoms formed into their most modern incarnation around 1000 years ago just as an fyi. If you want to stick with the 400 year date, it would likely be some other clan that unified the mountains first. As an idea (don't have to take it), maybe 400 years ago the old Lord of Appalachia rebelled or sided with House Deveram during House Ironwit's coup but House Delver sided with the Ironwits and as a reward for supporting them, the Delvers were given Lordship of Appalachia instead.

Also, I'd doubt that House Delver would be the ones to "kickstart" the mining industry since it'd likely be going on even before the clans unified, but they could have easily been the ones to do major reforms like organizing the mines, giving special rights and sending out survey teams of "Stonewhispers" or "Mountain Priests" (re: geologists) to find more veins.