I remember Mafia Members to be a thing. Though it might be an old and outdated one. See here:
Unskilled Mafia (Mafia) The Unskilled Mafia Member, is like a normal Member, but has only a 50% chance to succeed in killing his victim. The Unskilled Mafia doesn't know he is unskilled, nor do his team mates, and thinks he is a regular Mafia Member. (GAME 41)
The part of "thinks he is a regular Mafia Member" means that once we had Mafia Member as a simple Mafia role. Also this means that either all the three mafias are unskilled thinking they are regular MMs or some of them are regular MMs though there is no such role in the rulebook as you rightly pointed out. This could be a question for our hosts, ya know?
@Copy Panda Are regular Mafia Members an actual role for this game despite not being in the rule book or did you screw the Mafia over by giving them 3 50% kill chance roles? Not that I complain as that might increase the days this game might continue if night kills have an extra fail chance besides a doc stopping their kill. XD
I'd rather had a longer 100th match than a really short one.