I never really got to grips with bus scheduling, because you needed a masters degree in applied maths (or something) to fit the timetabling of the allocated buses (the easy bit, comparatively, which even I could do) in with the complex and convoluted set of agreements between the Transport and General Worker's Union and the London Transport Executive/Board without provoking a strike because you'd given a Shepherd's Bush crew one minute less than their entitled 40 minutes break! It was INCREDIBLY complicated, with no computerisation: one reason was that, although the peak hour extra buses were myriad on most of the major routes, the union only allowed a limited number of 'spreadover' duties per route and garage, a spreadover being where the crew work a.m then p.m. peak, and nothing else. These duties were, in any case, shorter overall so, from L.T.'s point of view, they got less work out of a crew. On the 12 around 1970 there'd probably have been about 25-30 buses that were only really needed for the peaks, spread over its four garages, so the simple solution would be to allocate 25-30 spreadover duties, which probably occurred in bus schedulers' dreams but nowhere else. If you were very lucky, you might get away with 8-10, which is one reason why, if you look at a full passenger timetable for a trunk route of the period (almost impossible to find, by the way, even at the time) there are so many 'short workings' at the fringes of the peak, either providing journeys that weren't really needed in order to keep crews busy, or (sometimes) the opposite, shortturning buses that were needed to the end of the route, but the crew were coming to the end of their maximum agreed shift. Don't forget, neither crews nor their buses could move from one route to another, either scheduled or unscheduled, during the course of a shift (with one or two very rare exceptions of long standing) neither could a crew be asked to work on another garage's bus on the same route, unlike Green Line. I don't know whether that provides an adequate answer to your question and, of course, I've forgotten most of what I learned then.