He prob had the guide made before the game even came out. I know I've had mine in a word doc 99% complete since last week since all the achievements are self-explanatory except for the chapter-specific ones and a couple Spartan Ops ones. I just was waiting till midnight MY time to put mine back up since it got taken down and add in all the youtube vids and the last couple descriptions, but seeing as this one is just fine there's no reason to have two on x360a. I'll stick with my walkthrough on TA. Good work OP.
Landed on exactly 500,000/500,000gs with exactly 18500 achievements and exactly 500 games. All 100% including DLC. Was going hard the first half of January to reach that goal! Finished it on 1-19-2016. Final achievement: Completion Serenity in Nero.