The only mentions of anything outside of Faerun proper by name that I've found so far is a mention of the Hordelands. Granted, there's a lot of reading to be done.
As part of a suggested outline for a Dalelands campaign featuring Moander:
"Levels 17–20. Moander manifests as a Blob of Annihilation to enter Myth Drannor and feed on the ancient magic of the broken city, becoming even more powerful."
I mean, that was basically his plan in the novel, but I...
As per page 238 of the PHB, all spell targets must have a clear path from the caster and can't have Total Cover. Which would make the first problem go away, although a magical scout is still a possibility.
It's been about a decade in-universe since we've had any updates, which seems to be that Unther conquered the the rest of Tymanther other than one city, and many dragonborn went to Calimshan as mercenaries.
I was thinking the same thing. You could easily use the same format to focus on 5 - 6 other areas for several books. I'd love to see this for Cormyr, or Thay, or Mulhorand
It also helps that there's not really more on them than their names. No alignments, nothing but examples of Mulhorandi deities, and that they are relatively benevolent. They just kind of leave it at that - saying that they are there, but virtually nothing else.
Compared to that tyrant Gilgeam...
The map covers basically the 1e/2e era maps - basically all of Faerûn outside the very southernmost coastal areas like Halruaa and Liuren (which get arrows and mentions, though).