halo 3 how do you know if you beat a mission in a certain difficulties of campaign?

[buddy]

do you know by the pictures in the lobby when choosing a start point?

 

[a Jose thing]

when you beat a level/mission in halo 3 there will be a loading screen that has the picture of Halo.
and when you pick the level/mission you want to start out with it should all be saved there in the lobby, you can start out at the beginning or at a saved point like for example (rally point alpha)