Here is my take on the 4 Ranks of librarian by level in the deathwatch rpg.

1-4 Lexicanium

5-8or9 Coidcer

Advanced class Epostilary

These are what i am working with as far as title goes in the game.

Any feedback would be awsome. I also want to know how to break down the chaplins and their title ranks.

Once again thanks for any feedback.

It seems reasonable if thats what you want to call them, GM makes the rules. but just in case you missed it I believe that the psychic powers section (184 core book, bottom left box) has a bit on ranks that states that basically everyone is a lexicanum unless the GM says otherwise (or with RoB presumably if they get the speciality rank) because codicier isnt just a status that you get when you level up, it is like a promotion that you might be the most powerful psyker in the universe but if you don't deserve the promotion you don't get it.

but as I said if the GM says otherwise then thats that, and those ranks seem reasonable to me

another way would be to use renown for it. Renown is a measure how other marines see the character. and gaining rank is much about gaining respect.