Actually we say the same thing. In PFM it is one column before Region IdRef as i noted but in TSV it is 2 before in O column as you've noted.
Though it should be obvious so far I repeat the procedure briefly:
Give a name which the game will identify in localised strings and place it in units table in the column before the one of Region IdRef (i think 2 before that in TSV). Here you can enter any name you like because it is gonna used only for this purpose. It won't be the name that will be appeared. Let's say you enter mickey_mouse and you want on screen to have Bavarian Line Infantry.
Go in your localisation.loc and make three new lines entering in columns A, B, C:
1. units_on_screen_name_mickey_mouse | Bavarian Line Infantry | False
2. unit_description_texts_description_text_mickey_mouse |a small text for the first short paragraph of unit card | False
3. unit_description_texts_long_description_text_mickey_mouse | longer text for the rest infos in unit card | False
It is supposing that for generic units (e.g. generic line infantry) you repeat the same name in units table but for units you want to add specific historic info you make a new name. In long description start your text with code \n\n so an empty line is placed add a new paragraph after short description.