Campaign Confusion *SPOILERS*

NOTE: I will not be using spoiler tags, so get out if you have a problem with that.

I am extremely confused with how the campaign is going to be working chronologically. This post refers to the following two videos:

Item A: E3 2012 Campaign Footage

Item B: Frank Playing Mission 3: Forerunner

The problem is that I can’t seem to figure out which mission comes first. Here are a few points that make no sense to me:

-In A, Cortana and Chief do not know who/what the Prometheans are. In B, Chief is fighting them and Cortana is referring to them as Prometheans.

-The ending of B shows us a cryptum in some sort of chamber, but in A the cryptum is flying on the surface of Requiem.

-In A, Infinity is crash landing on Requiem, but in B Cortana is trying to tel Del Rio to steer clear of the planet.

-Item A makes it blatantly obvious the Light Rifle dropped on the ground is a new and unknown weapon, yet in B, Chief is just wielding a Light Rifle like its old news.

So how does Cortana go from knowing what the Prometheans are and warning the Infinity to not knowing what they are when the Infinity is landing, or vice versa?

A lot of stuff was changed for the E3 demo, meaning a lot of what was seen will happen earlier in the game, but in different environments.

If I remember correctly, I believe Franky said somewhere that the E3 trailer was edited to make it seem like this was our first encounter with the Promethians. I may be wrong OP, but im pretty sure that is the case.

The E3 gameplay was modified. The level shown in the E3 gameplay comes AFTER mission 3. They just edited it so people would get what was going on.

Frank played mission 3.

E3 showed mission 4, heavily modified to make a great first appearance of the Prometheans as if it was really the first time. The final mission is much different, E3 demo was modified for E3.