That’s ok, because virtually nothing Gatsby told Nick about himself was true. For example, the yachtsman/mentor story was nothing more than a version of Horatio Alger’s “Ragged Dick” stories -— swallowed whole, it appears, by midwestern, naive and somewhat bigoted Nick (although, to give him credit, he DID see through the Albanian medal story -— “little” Albania did not exist as a country when the medal was supposedly given).
I’ve seen all the movies thought the latest was by far superior to the others in terms of presenting the era and staying true to the book.