In the recent post on Waypoint by Postums, it was said that players who log into MCC between October 29th thru October 31st would earn the spooky animated nameplate, “Happy Haloween!” (It’s a pumpkin with flashes of lightning). I got on the game during October 31st (my time zone is EST) and completed a Halo 3 campaign playlist (Heavy Anticipation). It is now November 3rd, and the nameplate still does not appear in my player ID customizations and my game is on the current update that was just released which added 20th anniversary Xbox/Halo cosmetics to Halo 3.
Same, logged in on Halloween and no nameplate was to be found.