It's pretty well established that WotC owns the 2e stuff lock, stock and barrel, and there's no obligations of any sort to the original authors (who were paid at the time, and whose IP became TSRs IP)I wonder what the legality is of just using stuff that was in the old second edition. I imagine there would be issues if they released stuff word for word the same even if some customers would be happy with that since they don't have access to the original books. The authors of those books probably still have some legal rights to what they wrote for TSR even if WotC bought the company.
So how far away from the original content do they have to get to avoid any legal issues? Could that be part of the issue with why these revisiting old setting books are so thin on the ground.