Late Roman Unit Sizes

[Robert Vermaat]

So, an hypothetical career of a military unit could be (just an example to describe my point):
1. deployed as a numerus of 1000 men and 500 cavalry in the west (~240AD)
2. the unit is splitted and send to different locations, later on parts of the parent regiment is filled up again (~300)
3. the smaller detachment (500 strong) is taken immediately to the imperial field army and now called auxilia palatina. The other unit is stationed near the danube and responsible to man several towers and to ensure communication with riders.
4. after the loss of a field battle our numerus near the danube is taken to the remaining part of the field army (~378)
5. 425/430AD the Notitia lists 2 units of the same name - the unit in the west is an auxilium palatinum - the other unit in the east is classified as pseudocomitatenses as therefore most likely already referred to as legio.
6. 60 years later the unit appears as αριθμος των λεγεώνων (numerus legionum) with +/-1000 infantry and 4-500 cavalry. 

I Always had my doubts about the origins of the auxilia palatina being among the old auxilia cohorts of the army serving along the borders.
Somehow I can't imagine how an old unit, once raised among foreign tribes but probably long-since filled with Roman replacements, is suddenly rised not only to a position apparently above all the other army regiments, but given a new name as well and a 'palatial' association to boot!
If (as you pointed out) the training of the auxilia was below the level of the training of the legions, why are these few units picked and upgraded while others of the same name go the 'normal' way of upgraded limitanei units and only get to be listed as pseudocomitatenses?
For me, the origin of the auxilia palatinae is far more easily explained as totally newly-founded elite units.