How did Vanilla RTW have multiple types of rebel generals?

[Cullhwch]

I noticed that in EB, after a faction is killed, all of its generals turn into Brihentin. Now, I haven't played Vanilla in quite some time thanks to you magnificent bastards, but wasn't there some sort of system that determined the bodyguards that went to rebel generals? I can remember a generic barbarian bodyguard, an armored barbarian bodyguard, a Greek one, and an early Eastern one.

Now, the Brihentin thing makes sense to me due to the relative abundance of Celtic rebel settlements (I believe that they used to turn into Carthaginian bodyguards) and the only other real choice would be a generic Hetairoi/Lonchophoroi bodyguard (due to the # of Greek colonies). Was there a real method to this or did one general unit have to have the slave ownership?