Apparently, the confusion over which evil group Modulok belonged to wasn't limited to the cartoon. In the original unpublished version of "The Treachery Of Modulok", Hordak and the Evil Horde are completely missing from the story. After the book was initially scripted and drawn, the decision was made to go back and tie Hordak into the story. The book had to be completely redrawn to reflect Modulok's change in allegiance.
Here are the surviving original versions of the book's final 5 pages, followed by the published versions: