It wasn't as bad as it sounds, as most of the secondary stock the dmus replaced was non-corridor, where once you were in a compartment that was it, no spreading around. Plus it was unusual to find a dmu more than half-full, they were commonly made up into formations well beyond what we now have. I've been reading the thread about overcrowding on the North Wales Coast line currently, where some formations are being turned out 2-car. I remember when this line changed over, quite late, about 1965, to dmus. Normally 6-car, and quite often 8. Control seemed to have a good idea of how services loaded, even looked out of the window at the weather, and allocated stock accordingly. Nowadays a 2-car or a 3-car is just sent out on an all day diagram regardless.