Manuscript Credit Switch

I understood everything about this story, even with all the twists and turns. One thing threw me at the very end however. If Marcus wrote a new book after the first Harry Querbert affair novel which explained THE TRUTH about the Harry Quebert affair, then wouldn't the book have been about Harry passing himself of as the author of The Origin of Evil? If so, then how is it that his real manuscript, The Seagulls of Sommerdale was then credited to Luther? Did Marcus make that lie up to save his old friend Harry's reputation?