The Lost Hero, The Son of Neptune, The House of Hades, The Mark of Athena, and The Blood of Olympus are NOT part of Percy Jackson and the Olympians. They are a completely different series called "The Heroes of Olympus.
This is because Rick added new characters so the books are not told from Percy's P.O.V
This is because Rick added new characters so the books are not told from Percy's P.O.V
I hoped this helped.