Late Roman Field Armies

[Flavivs Aetivs]

The Notitia provides a sort of snapshot of the military organisation at an uncertain period (perhaps several periods combined).

It is. The Comes Dalmatae command isn't first attested until 402. The "Magister Militum" command structure changes under Constantius III (and again under Aetius). The Spanish army was probably destroyed between 409-414. Elements of the Spanish and British armies were moved into the Gallic army during the Notitia's timeframe. Finally, the Placidi Valentiniani Felices gives us the last date of edit, which is 419 or 425 according to AHM Jones (however I have seen suggestions of 428 by other authors).