Re: Extra sections

There were never "sections" of an extra. Each extra was on its own, but could make multiple trips on the same day. Sometimes a crew was required to check the train register for an extra signing with a specific train order to be sure they had the right trip of the eame engine.
There were also "work extras" that could operate in either direction within set limits. These trains were usually the lowest in superiority and had to protect or clear against everyone else - unless otherwise specified by train order. Being instructed to "work between" two points nowadays authorizes a train to move either direction at speed; or joint with everyone at restricted speed.
A dispatcher could not authorize more than one extra unless they were protected from each other. If authorized in the same direction, generally no problem, the flagman protected against rear-enders. If opposing each other, then they had to have a designated meeting place if their limits overlapped. A dispatcher could give an extra "right" over some or all trains. They could also give them a "time order", effectively a one time use schedule that inferior trains could advance against them if they could clear in time.
SP's former Modoc line (mostly the old N-C-O) had several timetables only listing trains (second class?) in one direction, evenly spaced. At first this may seem odd, but was actually commonly used. Any train can be assigned any unused valid schedule at its initial station. For example:
The timetable for a division lists only 3 westbound trains departing at 8 hour intervals. If the dispatcher needs to, they can 1) run more than one section on a schedule 2) issue an order stating that train 363 departing Hipass (date) runs 2 hours late 3) annul (cancel) an unused schedule for that day. In this example, all the eastbound trains (not having a schedule) would run as extras. Extras being inferior to regular trains, they would be required to clear for the scheduled westbounds.
Each train affected would get the same orders. Everyone would know if an any train had been given right (superiority) over them, or if a regular train was annulled or was instructed to run late on its schedule. The superior train being restricted always had to have its order issued first.
Train orders can be extremely confusing. If issued improperly, misunderstood or ignored, they often lead to disaster. The biggest advantage was that trains could often still continue to run even if communications were lost.
I'm not aware of any major operation still authorizing trains to operate by timetable schedule, but I believe that some may still use a simplified form of train orders. Out west, Track Warrant Control (TWC) is commonly used on dark territory (no signals) or ABS. It is in effect a simplified train order, and a computer prevents most dispatching errors. Most railroads have removed the class lights from their engines.