The staff Working Timetables (WTTs) give details of the headcodes to be displayed, each volume having a summary in the introduction, with the actual headcode for each individual train given in the tables themselves.
On the North Eastern Region, the WTTs were issued in eleven sections: A through L (there was no section I).
Below are an example from each section, with the cover, the map of the area covered, and the pages with the headcode summaries being shown.
These were from a 'combined volume' version containing all sections, which made some pages hard to scan.