User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4902593-20130102114355/@comment-4430596-20130102142907

I may be misremembering this, but I thought in the Lightning Thief, the Nereid tells Percy that Houdini could, "Escape even the depths of Tartarus," which would imply he has been there. Saying that Nico is the first mortal to escape may be an oversight by Rick.