User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4547258-20130218180044/@comment-3146930-20130220000751

Well they didn't even say the entire prophecy until The Last Olympian, with only a few hints about it in the previous book. I mean we start really getting into it in The Sea of Monsters so it wouldn't be that hard to introduce the Great Prophecy