Okay, that explains it.
Hmm, I wonder what that says about DC's TOS Volume 2 and TNG, then. They both ran for 80 regular issues and, let's see, 78 months for TOS and 77 months for TNG (they did some brief biweekly runs in there). So maybe they finished one 5-year contract and got cancelled not quite a third of the way through the second one? Or could it have been, say, an 80-month contract that wasn't renewed?