A newer version of my North map - I still have some more geography tweaks to do before I start adding terrain. I finally finished all the hills on the Mainland (have two of the Moonshaes yet to finish).
It actually has been way extended - in my layered version, I have the 2e map of the Realms underneath this. The 3e Realms map shows how far the forest extended (which is how I kept it). Hellgate Keep will be on that hill at the very NE corner of the forest - it used to be quite some ways from the woods.
I think you could have extended the forest from the High Forest to Anauroch after the end of Hellgate keep didn't the treants start moving the forest east again?