Mark came over to Alexandria, bringing his own υπομνηματα and that of Peter, from which he transferred to his former book the things suitable to whatever makes for progress toward knowledge [Clement, to Theodore I.18 - 20]
It had long been speculated that Justin's "memoirs of the apostles" (ἀπομνημονεύματα τῶν ἀποστόλων) was a harmony of the Synoptic Gospels; that this collection of "memoirs" has agreements — including some harmonizations — with the Diatessaron reinforces the view that it was a harmony. The discovery of textual dependence raises the possibility that Tatian incorporated parts of Justin's ἀπομνημονεύματα into his Diatessaron, perhaps even using it as a foundation [William Petersen in Bart Ehrman, Michael Williams Holmes The State of the New Testament in Contemporary Research p. 89, 90]
Tatian, accordingly, was wont to transfer, from one [gospel] account to another, the smallest of items, and that, too, no matter how remote these items were, in the orginal sources, from the material into which they were to be inserted. [Hobson, the Diatessaron of Tatian and the Synoptic Problem p. 58]
I can't believe people can argue that the idea that Morton Smith forged the letter to Theodore is the most likely possibility here when Smith never once referenced the idea of the 'secret gospel' being described in the letter might have been related to the Diatessaronic tradition. It was a glaring oversight on Smith's part and those of his critics. I would argue that the idea that Mark developed a longer text out of two υπομνηματα which turns out to be a primitive ancestor of surviving Diatessaronic 'harmonies' is the most likely explanation for the contents of the letter to Theodore. People should be debating this rather than all these meaningless comparisons with canonical Mark. Where has any of this led? What has any of this proved? Other than of course served the other side well in bringing any meaningful research into the discovery to a grinding halt.
