I am trying to run a report to view bad emails within our Marketo instance, but I'm finding that an email could be listed as bad, but is not categorized as unsubscribed, invalid, or blacklisted, what other reason could there be for them being in a report?

During our account setup, I created a group of smart lists on deliverability and list "health." The lists include:All Hard and Soft BouncesCustomer Complaint Received by ISPHard Bounce Category 1 - SpamHard Bounce Category 2 - Email InvalidHard Bounce Category 4 - Technical IssuesSoft BouncesIf you haven't set these up, I'd suggest you do so you have a good foundation to look into the "bad emails" you refer to. Happy to show how these lists were built.