Some older stuff, like the Creepy posts we had before the shutdown, were single stories from a larger book. Also, stories from serialized Manga anthologies and trade paperbacks are no longer acceptable under these rules - they're single stories from a larger volume.
I'm really against only posting a third of a self-contained story in a magazine or book. I'd explain further but I'm about to leave. Maybe I'll have a better explanation after I come back.