Interestingly, Halo: The Fall of Reach actually was published before Halo: Combat Evolved came out. Under Bungie, the hierarchy of Halo lore looked something like this: Game Lore > Book Lore > Misc. Lore. However, the community always treated all three as mostly equal. When Bungie launched Halo: Reach, the lore community was pretty upset because the very foundation of Halo's lore was retconned. They claimed that both worked together, but the community didn't have enough information until 343i started feeding the community helpful, connecting information.