You don't know that. No one knows about that except for people working at Bungie. They could very easily churn out 10 more Halo games. I remember a documentary on the Making of Halo 2, where they said they have over 100 years of Halo fiction already written out. I doubt they're gonna do just one more game and throw the remaining 90 years of storyline out.
Might be talking about the back story for the books... have you read em all? there pretty good.
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