Yes, you heard me correctly!
There apparently was a Mystara book for AD&D 2e that was never released!
To Wizards of the Coast:This is what the Petition on Change.org is asking from Wizards of the Coast!
We ask that you please release the unpublished manuscript of the by Jeff Grubb. We suggest either posting the PDF as a free promotional item of "historical interest" in a DRAGON+ magazine article, and/or at the Vaults of Pandius (the official Mystara fan-site), and/or posting it for sale at DMs Guild.
Thanks for considering,
-World of Mystara enthusiasts
For those who just want to read: