Offfically, all Pennsy freight services were operated as extra movements carrying no timetable authority. However, the freight schedules were usually listed in the employee timetables for the regions(s)/division(s) in question under "Arranged Freight Train Serice" not far behind the line descriptions and passenger schedules at the front of the booklet.
As a general rule, freights ran much closer to the posted schedules on the smaller divisions/regions, such as the Northern (former Williamsport and Buffalo Divisions). Second sections were rare except on the main lines in times of prosperity, and they were usually designated by letter (e. g: SW-6A & SW-6B), During the Vietnam buildup of 1964-1966, the PRR often operated its primary eastbound runs in multiple sections, but the empties usually went west as unsymbolled extras.
A good starting point would be Jerry Britton's "Keystone Crossings" web site, which has a huge store of PRR info; Here's a link:
http://kc.pennsyrr.com/
