I'm in the early stages of working on a possible historical sourcebook for the DMs Guild that focuses on the relatively narrow window of time between when the green and dark elves first traveled to Toril and when the gold and silver elf refugees from Tintageer appeared.
There's not much in the Grand History of the Realms except the approximate dates both groups arrived. Are there any other books that describe those ~2500 years in any detail, or is it pretty much 'make up whatever feels appropriate to the lore' territory?
Of the sourcebooks, there are Evermeet and Cormanthyr. But there's indeed some lore in novels. And many small treats from Greenwood himself. Specifically on the ancient green & dark elves (...and how it all went downhill): in 2007 thread. Most of such scattered lore (including this bit) is compiled in "So saith Ed" files in the Keep archives. In PDF, so knowing your way around pdfgrep helps a lot.
People never wonder How the world goes round -Helloween And even I make no pretense Of having more than common sense -R.W.Wood It's not good, Eric. It's a gazebo. -Ed Whitchurch