Basically the Extended Offices Mod V.2.1b gives you legionary ancillary since the beginning of the game (Camillan era) allowing you to have one legion for every three provinces conquered. Tha ancillaries look all the same, they differs only by legion number inscribed on them and gives you the names (in the ancillary description) in no particular order, just to keep track of your legions. Suitable for role-playing campaigns that do not dwell too strictly on historical timelines.

The Extended Offices Mod V.2.2 gives you beautiful RS ancillaries for legions from Marian era onwards, with detailed historical descriptions matching the regions where each particular legion was originally raised or deployed. Suitable for those who love to re-play/re-create historical Roman Empire.

In other respects the versions are identical IIRC.

You could also download both, check the files and than decide which suits more to your preferences and install that one.