
Originally Posted by
PerXX
The various unit styles, Feudal, Early Professional, Late Professional and so on doesn't hint on when they might be available, even though it might sound that way. They represent the various way they are recruited.
For instance, Feudal units are expensive in upkeep, and take a long time to replenish, but are possible to hire in a single turn, representing the fact that they already exist, and are then called into the Kings service.
Late professionels replenish quickly and have a fairly low upkeep usually, but often take many turns to hire, representing that they are not already running around the kingdom, but needs to be trained up first.
The Byzantines for the most part didn't implement the feudal system that most of europe used, but rather used an army of professionel trained troops, much like the europeans used later on. Hence many of their units fit under the "Late Professionel" status.
I'm sure you could get a more detailed explanation in the RR/RC submod forum, as thats where it got implemented, but that's generally the basics of it. It's various different way to recruit the unit, rather than indication of the age the unit should be available.