Schizo may have a point in some regards.(if I get what you are saying , then in fact BUNGIE did break canon in an event)
S1l3nt V1p3r-- I have a friend with a modded XBOX and he has played REACH while I was there. I can tell you with 100% certainty that they did in fact change an event
completely from the book. More than one event has changed in some regard, others have not.
They did however create a great back story that lines up and makes sense for Noble team members. It's a great game, great visuals, and the multiplayer is phenomonal!!
Ps-I am not about to go in details for sake of a pointless arguement that would be spoilers. Its a GREAT game, but IMO....good have been even better