Late Roman Unit Sizes

[Nathan Ross]

either five units, six units or seven units. Why is there so much difficulty?

As Evan says, it's seven. I haven't seen anyone credibly suggesting otherwise - where did the alternative figures come from?

The evidence continues to mount for the Lancearii being legionaries or being an integral part of a legion.

Legions did contain lanciarii, from the early third century at least. The Lanciari of the ND were legionaries too, and as I've said there were lanciarii in the imperial comitatus of the tetrarchic period.

However, the legions mentioned in the Panopolis papyri (cAD300) were old-style frontier formations, still apparently using the Severan model, so not surprisingly they seem to feature integral lanciarii and equites. Whether this same model endured even much further into the 4th century is unknown, but it can't be used to work out the structure of later Roman legions more generally, still less those of the imperial field armies.

Luke Ueda-Sarson, meanwhile, has a page about lanciarii here that you might find interesting.