Here is an interesting comparison of Cortana over the course of the 4 halo games:
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Limited Edition Halo 4 Copy
As soon as you wake up on Dawn, look around the Cryo room and you should see two or three Halo 4 Limited Edition Copies on the floor.
There are a also a few more scattered copies around the map like on the ramp where you can assassinate the Elite on the ramp control center shown in the video below.