Running Sections on the SP

I checked my old rule books and clearly at least on the old SP you could run any class train in sections.
My favorite was "second 76". Frequently, the Lark (first class train 76) with it's Pullmans would leave San Francisco's Third and Townsend flying green flags. And some time later that night a non-descript drag freight would ease out of Bayshore yard as Second 76 for a slow all night run to Watsonville Junction....less than 100 miles. It always intrigued me why the dispatcher did it that way, since "Second 76" was hardly any kind of first class train. But at that point there were no scheduled freights (third class trains), so obviously he used the tools he had to simplify his dispatching.
In a lot of the old timetables you find three third class trains scheduled roughly eight hours appart in (only) one direction on a line. From bits and pieces I have learned, apparently all freights in that direction were run as various sections of those schedules. Apparently by making them "scheduled" trains, it automatically gave them superiority over the extra trains being run in the opposide direction, saving a bit a work it telling crews which trains had to take the siding at meets, etc. It probably also saved a "run extra" order since only a clearance was needed. Keep in mind that "scheduled train" in this context meant authority to run, and had little to do with the actual times. The scheduled times were good for 12 hours, so as long as a train was less than 12 hours "late" it could retain authority to run on the assigned "schedule". Since these trains were not really running on any schedule, if one was needed to facilitate opposing traffic, the DS would use "wait" orders to create a "schedule", same as he would have to do for extras. My guess is that was the kind of dispatching Les was describing above.
Trainorder dispatching was truly an art form. I hope I got the above right since I was never a dispatcher, I was always on the receiving end executing the orders.