My thoughts exactly. Selucid or Gaulish Cohorts make my eyes bleed. Velites, Princeps after Marius make little historical sense. Unless of course there is an event the player chose to say no about this issue.
I know this might sound nit picking but there is something unholy in Caesar´s army being made of Avernian princeps or Trevian equites. Gaul has just fallen to rome and troops raised there would certainly not follow such naming. Culture and assimilation should have a say here. During this time Caesar only raised one "Gaulish" legion at the V Alaudae, but that was done in Transalpine Gaul which had been under roman control for over 150 years.
Question, how long would it take a stationary cohort to loose this veteran status?
All that said I have preordered the game already