In the meanwhile of my drafting the previous response to Bellisario, Messrs. Swan and Hays have already forced Bellisario to admit that there is no new revelation. Accordingly, he has attempted to rely on a yet more flimsy branch. That flimsy branch is essentially that there are oral teachings of Jesus that were not placed into Scripture but were otherwise handed down to us via the Apostles.
This is, effectively, Bellisario's last gasp in the discussion, since he cannot demonstrate the apostolicity (let alone the divine origin) of any doctrine not found in Scripture. He has no good reason for thinking that there are any such doctrines, has no positive argument to offer in defense of oral traditions, so he's left with arguments like, "Where does Jesus say that now all of His Word would be in written form only?"