Some quick thoughts on dwarven history:
Gaz 6 wrote:BC 1500:The Nithian culture begins its rise in the lands east of Rockhome. They perform no exploration in the west and never encounter the dwarves.
BC 1400: Denwarf discovers the great cavern he calls Dengar and decides his time is done. He disappears into the lower caverns. The second dwarven king, Everast I, is crowned. The dwarves begin to build their greatest city within the Dengar cavern.
BC 1000:In the time of the eleventh dwarven king, Blystar III, nonhuman tribal movements put marauding tribes of orcs and goblins against the dwarves. This is the same tribal movement wave that sends the gnolls into ancient Traldar lands in what is now modern Karameikis.
BC 500:The eastern Nithian culture is destroyed and ereased from the minds of man by vengeful Immortals.
BC 492:The Rockhome borders are finally secured against the nonhumans in the Battle of Sardal Pass. This is Year 0 in the dwarven calendar.
BC 475:The dwarves begin a program of exploration outside of Rockhome. They meet Alasiyan nomads and begin to trade with them.
Gaz 8 wrote:BC 938:The Fall of Hindon; orcs burn the Elderhall. The Dark Years begin. Dwarves and orcs fight for control of the halfling land, in battles of Bloody Sands (936), Fireaxe Field (932), and the Hill of Cold Teeth (930).
BC 929: Dwarven rule begins. Loktal Ironshield crowned King of the Glittering Land. Hin enslaved. Dwarven kingdom grows rich, attracting orc and human invasions that weaken the dwarves.
So a couple of high level thoughts.
1) One of the big points that Gaz 6 makes, that Rockhome dwarves and Nithians never met each other, is IMO utter garbage. That statement is clearly disproven by the Gaz 8 timeline which indicates that dwarves (under Loktal Ironshield) ruled hin lands circa BC 1000... a time at which the Nithian empire was at its height in the Known World! I find it much more likely that Rockhome and Nithia knew about each other (and probably interacted through trade, skirmishes, etc), and that the dwarves forgot about this after the SoO was cast in BC 500.
2) There appear to be several possible waves of dwarven expansion/exploration from Rockhome. If the dwarves and Nithians did know about each other, and did interact (as I am going to assume), and
if the Nithians did also colonize the Savage Coast, then I think it is also safe to assume that dwarves could have gone with them in that first wave. So we might have something that looks like this:
Early dwarven explorers leave alongside Nithians to explore the western coast of Brun, including the Savage Coast.
Dwarven expansion begins. Dwarves conquer nearby territories including hin lands to the south.
The SoO is cast and many dwarves outside of Rockhome, loose a majority of their history (assuming that their expansions beyond Rockhome were so closely tied with Nithian allies, that the history of the two peoples could not be separated). Thus we end up with a bunch of dwarven populations across the KW and beyond, and have "no" explanation for how they got there.
"Modern" dwarven exploration begins. This could have in fact been spurred by the desire to reconnect with all of these external, and "mysterious", dwarven populations already outside of Rockhome.
So... getting back to Koralgesh (which sounds like a Nithian influenced name to me...), my bet is that dwarves probably established the settlement along with Nithian allies as far back as BC 1500. If you don't like a date that old, it is also reasonable to assume that they expanded into that area circa BC 1000, at the same time other dwarven kingdoms were popping up outside of Rockhome. In this case it is still very likely that Nithains could have been involved as allies of some nature. Then post SoO dwarves could have rediscovered the settlement sometime after BC 475. In this case the "ruins" they were building over could have been Nithian, or they could have been dwarven (with Nithian influences).