Here is an interesting comparison of Cortana over the course of the 4 halo games:
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Level: Exodus (Rally Point Bravo)
Very far back in the map, there are two, maybe only one Marines standing on the platform you passed while in the Falcon killing the Covenant as you passed as well as defending the Marines as you pass. It seems these Marines stuck around and do still talk, and you are able to reach them by following the instructions in the video below.