I know of a glitch that gives you permanent followers from NPCs that are not designed to be followers, but only from the subset of NPCs that purposefully disappear. And I have seen no mention of this glitch on this forum and it wasn't corrected by the Unathorized Arcanum Patch. Is it truly unknown or am deluding myself to think that I discovered something in the less of year of play that others didn't discover in a decade of play?
Do you mean that bug where if an NPC object gets destroyed by script when in the PC's party, their portrait does not disappear?