Why should we accept the claim of a mutilated and many times rewritten source that the Marcionite text was so called? This information is not passed on through any of our other sources. The earliest use of the term τὸ ἀποστολικόν I can find is in the Eclogae Propheticae and it is used to describe the words of John the Baptist. The fact that Clement of Alexandria never once uses the term in any of his writings should open us up to the question of whether either this text or the Excerpts of Theodotus were really written by Clement or added to the collection because there were some blank pages needing to be filled.
Indeed τὸ ἀποστολικόν the neuter of αποστολικός often combined with the noun τεύχος or βιβλίον (‘book’, ‘volume’) and clearly came to mean a collection of New Testament Letters assembled in one volume by the fourth century. There is no doubt about this. So we see, in his edition of the Letters of Paul (CPG 3642) the deacon Euthalius, who lived in the fourth century ad, speaks of an ἀποστολικόν τεύχος. Yet are we really to believe that the orthodox start using the original Marcionite name of the Pauline collection?
I think a much more plausible explanation can be found. The Dialogues are also usually dated to the fourth century. Couldn't the use of the term τὸ ἀποστολικόν merely be a reflection of the language of fourth century ecclesiastical circles that the Dialogues of Adamantius were written? Or perhaps the authors overall anti-Origenistic worldview?
I will stop calling the Marcionite collection of Pauline letters 'the apostolikon' from now on.
