"Since the use of the accusative [with prepositions] increased sharply in the centuries after Clement's work, and that of the dative declined even more sharply, the high relative frequency of accusatives in the letter would be a trait almost certain to be found in a later imitation; it seems to me the chief ground for doubting the letter's authenticity [Morton Smith, Clement of Alexandria and a Secret Gospel of Mark p. 74]
On the other side, a particularly impressive correspondence is the citation of Proverbs 26:5 not according to the Septuagint (ἀποκρίνου ἄφρονι πρὸς τὴν ἐκείνου ἀφροσύνην αὐτῷ) but in the wording that Clement quotes in his Stromata 5.3.18.5 (11338.8 — 9 Stàhlin) ἀποκρίνου τῷ μωρῷ ἐκ τῆς μωρίας αὐτοῦ. [Saul Levin, “The Early History of Christianity, in Light of the 'Secret Gospel' of Mark,” Aufstieg und Niedergang des romischen Welt 2.25.6]
dating back to conversations with his grandfather, Gaston Frank. "He said we represent one of the last descendants of the Frankist Jewish faith in the world," he muses. "I grew up thinking that our family was something like the Last of the Mohicans."