Folks just don't seem to get it. Not quite so good as saying that they were added onto the end, which would be a bit less trouble, but not a bad theory. So what would confirm the theory but sayings added into the sequences known from Oxyrhynchus. There aren't any. The fact that sayings are not added into the sequences known from Oxyrhynchus.
People just state the theory anyhow, as though self-evident.
Some sayings may well have been added later. Bill Arnal suggested this already. Bits is the key word. Go ahead and debate. Then it got left out in GTh Cpt.