Late Roman Unit Sizes

[Nathan Ross]

to a quartermaster and then the chief of legion paperwork, likely including pay.

I don't think so - aren't you thinking of the actuarius or adiutor? The campidoctores were fighting men - those of the Gallic legions led the sally during the siege of Amida, and were later commemorated by statues in full armour at Edessa. Campidoctores are often mentioned among the principal officers of the legion, and appear in crowning ceremonies of later emperors, including Leo and I think Anastasius. They were certainly not mere chief clerks or quartermasters! They were either very senior veteran soldiers or a grade of centurion/ordinarius.