Me too.
I tested some options and i guess it is like we said before.
You have to complete every campaign to itself. Like -> Completion, gather all codex's, gather all field manuals.
It would be enough when you have just to complete the last campaign map with one codex / field manual left.
Except the fucking flying mission. On that it could be cool if it's not the last codex you have left
EDIT:
Just one hint for you guys: Trophy "Airborne Cannons"
-> Delete the Game, reinstall without update the game. Play those Fly-Campaign -> Last Map -> Airborne Cannons - Trophy is really easy. Got it in the first attempt.