So I'm looking through "So Saith Ed" archive for all info I can glean on anything asked about Baldur's Gate, and in the 2004 archives he is bound by a lot of NDAs due to some project.
It's now 2013...is he still bound by NDA and...what was the project? If it's scrapped then...well, there's nothing we can do I guess since NDA doesn't seem to have a time limit (or do they? NDA should have a time limit).
Now I haven't scanned the other archives yet so for all I know, he may have gone into more detail in the later archives.
So think of it like this. Ed doesn't own the Realms any more. Hasbro does. I'd imagine that everything about the Realms is NDA in perpetuity. Ed is still able to dole out plenty of Realms lore though because quite frankly he can just make stuff up as he goes and people will take it as lore from the source....which it is. But when it comes to established lore, places, and characters, I am sure there are pretty strict constraints on what he can and can't say.