Bob and all,
When you consider how all that detail and data were handled back then, the degree of ORER accuracy is barely short of miraculous.
It was all done in the "BC" era - before computers.
Everything was written up on paper reports, typed and kept in the road's roster files, often using the roads own car classification system.
These would be the resource for the ORER which were then retyped (no speedy copier machines back then), proofread, corrected and/or retyped if need be, and put into the ICC/AAR car classification system used by the ORER.
All this was in long lists that had to be reviewed and checked several times for accuracy before submission to the ORER for printing.
No telling how many times if there may have been a gap or error because some report had not completed the rounds, or something got lost., or was omitted, that an 'educated guess' likely was used, with a note to correct it for the next issue - if recalled.
Ah, yes! Typing all that up (with carbon copies) on a good old Underwood Model 5. . . .