So I got in touch with Scott over at DriveThruRPG to find out whether I'd messed up the files for the hardcover of Heroes Against Darkness, and I got this quick response:
"No, that isn't normal at all. It should take about a week at the outside. I'll send along an inquiry to our client rep over at LSI and see if she can track this down for you."
And like magic, today the print files are approved! I've ordered proofs of the softcover and hardcovers, which I hope will arrive before Christmas. Once I've checked them out I'll make them available on DriveThruRPG.