I get it. But that's not the point.
I’m just thinking in alternative for the recruitment of mercenaries without being too much attached on historical facts. I believe thats possible just by giving more focus to the mercenaries hiring system than to where these mercenaries were found. For Total War is about alternative history based on facts not true historical reenactment (my opinion).
Why can’t I recruit these Galatians Celts in the territory immediately adjacent to Egypt in Anabataea? Since these Celts probably offered themselves as mercenaries in that region too but were not recruited.
In addition, what if I’m playing with Ptolemaioi and expanded the Empire to regions that historical empire never arrived, these Celts couldn’t offer themselves as mercenaries in these new regions?
In my view, AoR units are a result of the society, culture and environment of a specific region and mercenaries are AoR units that left their homeland to fight anywhere for those who paid as far the recruiter knew of their existence (maybe by being aware of their home land, not necessary being at their home land).
I'm not sure how the auxiliaries recruitment system work but the fact that I have to use a general to carry the Yemeni Archer in the Arabian peninsula to fight in Britannia bothers me a bit. It looks like they cannot walk by themselves.
Anyway, it’s just a suggestion.