For a while in 1990 in June at the time of the State Examinations and indeed the World Cup (Italia '90) there was a temporary agreement that if no conductor was available, rush hour services would be covered by a driver who would not collect any fares!
I hate to be a pedantic Pat, GNR but the 36 would have been OPO through Drumcondra, albeit as a single decker so I take your point as regards the Double decked 33b. Of course there was still the odd 33 TPO service through Portrane just to confuse things slightly, at 7.30 (?) outbound in the morning to Skerries, the early 'workman' which wasn't officially on the timetable and one inbound leaving Balbriggan in the afternoon. Gosh, once upon a time I could remember those timetables.