Nailed it. And not far off how Greyhound worked. The Vancouver - Seattle buses were supposed to be in a "Strict Pool" due to the fact that only enough buses had the PTB plate for their operating license in BC. But on more than one occasion I'd service a bus that wasn't plated for BC.....meanwhile I'd book a PTB plated GLI bus into the system and see it had been bouncing around California all over the place. But alas, only some drivers I knew actually noted the lack of plate but were forced to take the bus anyways.
Buses that were actually decent caused some drivers to play dirty. If one driver came in on a sched with a good bus. And the guy behind him who finished after had a crap bus, that guy behind would end up taking that first driver's bus as he would then be the first one out before the first guy who was going out later. So the guy going out later would end up with the other driver's crap bus that maybe would make it back.