Late Roman Unit Sizes

[Nathan Ross]

just wanted to make a point about use of evidence that is not of the period in question

Of course. And also of course Ammianus's perhaps vague military terminology - in this same section he mentions a 'cohort of cavalry'...

But as Isauria and Pamphylia were not garrisoned at all until the late 3rd century at the earliest, and trouble with the Isaurians apparently continued into the early 6th century, I would think it a safe bet that strong limitanei forces remained there throughout the period in question.