Continuity mistake: During the assault on Cote d' Azur, James loses his left arm from the elbow down due to a plasma charge from a Covenant Hunter. A few moments later it says he manages to salute with his left hand.
Other mistake: When Corporal Harland asked John how to become a spartan, John had thought that they had been picked twenty five years ago. They had been picked thirty five years ago; not twenty five. Dr. Halsey also says twenty five years ago in the book. The Spartans had been chosen in 2517 and it was 2552.