I thought perhaps it may have been mentioned in the Shadowstone Chronicles or Loremaster Legacy, which I have purchased but not yet had time to read.
I don't recall it being mentioned in Loremaster Legacy. I am a bit confused by the mention of Shadowstone Chronicles OR Loremaster Legacy, because Loremaster Legacy is book 1 of the Shadowstone Chronicles series. Book 2 isn't out yet.
Loremaster Legacy doesn't have anything set in or near the Xaar region to my recollection. Pretty much everything set on Jaiman is in Rhakhaan, with some references to Tanara, and a brief visit to the Forge.
Not to be snotty but only my novel is canon; the others were done without my knowledge or permission. Please treat them as you wish.
You don't sound snotty. I think it's pretty normal for the creator of a work to decide what is and isn't canon within the scope of that work.
ICE seems to face some pretty unique challenges owing to to copyright for a lot of their material not being owned by ICE anymore. I'm probably not expressing this well, but what I mean is all the books you guys can't republish because the rights reverted to the original writers. Not sure how much of that applies to ShadowWorld, but I do notice that only a few of the original modules are on DriveThruRPG. That must make the job of updating ShadowWorld for the modern age a lot harder.
I am a bit curious about the history here. Were the other books something ICE commissioned after you left in 1992? Never read them, but I do think the 1995 Curse of Kabis module was really way off in terms of Canon.
My overall feeling is that ICE didn't really know what to do with ShadowWorld after you left.