Besides the Faction column you also have to check the Culture column to see what factions really do get a particular unit.
ChivalricKnights are listed as CATHOLIC only.

One other thing I have noticed in unit stats is that for some units you have ALL_FACTIONS and for others you have NO_FACTION.
It seems region specific units such as Gallowglass and Highland Clansman have NO_FACTION. But in reality there dosn't seem to be a difference between the settings.