Changes in the Roman Army

[Frank]

Vegetius told his reader that he was using other authors works as part of his Epitome, most of those works are now sadly lost to us.

Speidel conjectured in an article about Vegetius' legion, that Vegetius probably had the same problem like modern historians. He found no exact figures in his sources, because ancient authors were very often not interested in such details,

So Vegetius started to design some figures which looked reasonable. For example, a contubernium must have a leader like in late empire, so we have a decanus and decanus means 10 men, with the decanus himself 11. 10 contubernia plus a centurio are 111, and so on ....
Fully wrong, but reasonable.

So yes, a lot of information Vegetius gives us about the ancient legion seems to be correct, but not the figures.