Diaglo, I am looking at your map. Unfortunately, it is rather too small, and there is no Land of the Red X in FR.
The Western Heartlands is a rather more limited area than what you named. We'd be looking at the area bordered in the north by the Delimbiyr River Valley, in the east by the Stormhorn and Giant's Run Mountains, in the south by the Cloud Peaks and the Snakewood, and in the west by the sea. This area hasn't been under too much scrutiny outside of novels. We got Volo's Guide to the Sword Coast and the High Moor & Serpent Hills booklet for Elminster's Ecologies. Volo is always more intent on detailing taverns and inns than dungeons, and the EE booklet was rather narrow in focus.
So, yeah, there are areas on the map that haven't been done. The Greenfields, Baldur's Gate, Trollbark Forest, Marsh of Chelimber, Reaching Wood, Forest of Wyrms, Iriaebor, Elturel, Berdusk... Loads of places that haven't been visited for years, if at all.
And just as an aside... The only two things Al-Qadim had in common with Anauroch was that they are on the same planet, and both have a lot of sand.