As far as I know all the BB sprockets have an outer guide plate. The early rear sprockets that ran on the early (silver) hub did not have an outer plate and the belt usually runs slightly off the edge of the sprocket. The later (black) hubs had sprockets with inner and outer guide plates fitted, although there is no real need for the outer one if it all tracks well. The inner guide plate prevents the belt rubbing on the tyre sidewall and must be fitted.
