Referring to Old Dawg's work on the GazF project (which admittedly I am not well versed with), we have the Genalleth and Geffronel elves eventually forming the elven clans that will live in Wendar. I'm pretty sure that the Genalleth are part of the second migration - meaning that they would not have been present in the north in Blackmoorian times, but the Geffronel seem to be in the Wendar area since the GRoF.

Given the similarity in names of these elven clans (Genander, Genalleth, and Geffronel) maybe it's possible that they all have some ancient common ancestry. In fact if the Genalleth are distant cousing of the Genander elves, then it would give them a great reason to want to leave Vulcania and find their lost brethren (whom they know live somewhere in the north).

This might mean that the Geffronel are actually be descendants (or an offshoot) of the Genander, and this would allow elves in the Known World region (I imagine that there is some contact between Wendar and the other nations of the Known World) to be descended directly from Blackmoorian elves.

Personally I would prefer it if the Wendar elves arrived on Brun via Skothar, being in fact direct descendants of the Blackmoor elves, but your version fits better with various fanon material.

In terms of reconciling things with canon, we have the situation where the elves do not begin building civilizations outside of their cradle on Davania before BC5000, while per Blackmoor canon there would have to have been Elves north of Thonia dating back to at least a few centuries before that. Acutally when you think about it, this boils down to how strict you want to be in you reading of canon. I could easily see the Blackmoor Elves as being results of early Evergrun/Fey experimentation with the Rainbow Bridge Magic, making possible instant travel between continents.

IMC I also have the Wilderlands Setting fully incorporated onto Pre-Cataclysmic Skothar meaning the elves of those lands also being of the same origins.

-Havard