How did foreign recruitment work exactly? What happened if one province had several foreign cores, for instance?
I believe you could recruit the lowest pip unit from a country that has the same artillery as you. Thus you would sometimes set your preferred artillery to be outdated in order for a cav or infantry unit you want to show up.
I'm not actually sure what happens if you have a province that happened to be a core of the Ottomans, France, and Russia who were all at the same tech level (i.e. same artillery). I suspect it would be the lowest pip unit (tiebreak factor unknown).