Creator Breakdown: Peter Laird put Volume 4 on hiatus and later sold the franchise to Viacom because he was burned out. Many posts on his blog reveal how, ever since the merchandising and cartoon started circa 1988, things spiraled out of control, and he ended up neglecting his own family. As part of the deal, Laird does have the option to produce 15 issues per year set in the Mirage continuity. He has written four issues since the sale, but he otherwise has little interest in pursuing it.
About half of the stories within Volume 1's Guest Era were originally written to fit in with established continuity and were treated as such by Mirage staffers. For example, "Sons of the Silent Age" is a follow-up to Rick Veitch's "The River" trilogy. However, due to rights and money issues with the independent creators, Mirage ultimately had to declare these stories non-canon.
There was apparently concern that this would be the case with Volume 1's eighth issue due to the presence of Cerebus the Aardvark. Mirage would've needed David Sim's permission to reprint the issue, and they feared he wouldn't give it, so a non-Cerebus version of the story was whipped up to fill the hole. Of course, this trope was averted in the end. Click here for a review of the Cerebus-less story and some of the back-and-forth that was involved.
Schedule Slip: All the time; during the first series the creators joked that you could tell it was a Mirage book if it was running late.