Tertullian reports in his polemic against Marcion's Gospel how Marcion himself complaint about those who must have nicked his text, plagiarised and published it, even before he himself could do so:
How absurd it would be that when we have proved ours the older, and that Marcion's has emerged later, ours should be taken to have been false before it had from the truth material, and Marcion's be believed to have suffered plagiarism through ours [Luke, or Matthew] before it [= Marcion’s] was even published:
This most important information of Tertullian has so far, if I am not mistaken, never been picked up by any scholar: Tertullian reports that Marcion – apparently still in his Antitheses – did explain that Luke (or is Tertullian referring this to Matthew?) was ‘plagiarism’ (aemulatio) of his own Gospel, and, even more importantly, that this plagiarism occurred even before Marcion had edited and published (editum) his own Gospel – which he seems to have done in conjunction with the Antitheses in which he drew attention to the unauthorised publication of the appropriated, interpolated and judaized version of his own Gospel.
From this information we have to draw that we are dealing not with only one version of Marcion’s Gospel, but with two different editions and possibly recensions!
The first was the unauthorised version of the Gospel which ‘suffered plagiarism’, must have gone out of the circle in which Marcion had distributed it, it was copied and altered. The text of this edition/recension which was obviously only intended for internal use, a so-called 'memorandum' or 'apomnemoneuma' can no longer be retrieved.
The second recension, the edition of which was undertaken by Marcion himself. In this Marcion responded already critically to the plagiarised version of his first edition, hence took notice of and potentially may have also revised his previous recension. Calling the altered version a ‘copy’, Marcion certainly acknowledged that the plagiarised product was based on his own, older text. The reason for himself to formally publish his own version, was of course the challenge by the plagiarised version. And in order to defend his own product, he added first the Antitheses and combined the Gospel with the ten Pauline letters, certainly not, as we can learn from this process, because he wanted to evangelize the world – and he certainly had never dreamt that his initial work would be further copied and eventually lead to the fourfold New Testament (and to harmonizations of it). Instead, his publication was a direct reaction against the case of plagiarism in self-defense. When Geoffrey M. Hahneman in his book on the Canon Muratori states that ‘Marcion’s basic intent appears to have been to recover a lost tradition’, we can certainly agree, but the quoted text of Tertullian goes against his further view that ‘there is no direct evidence that Marcion knew or excluded other gospels. So far as is known, Marcion never polemized against the other gospel traditions.’ Although we are not aware that Marcion knew of more than the one plagiarism, we do not know whether he is talking about Luke (it could also be Matthew, as Tertullian calles the latter often ‘our’ Gospel) or another version. Having said that Marcion, according to the above quote, was highly critical of the copy made of his Gospel, to the extent that he wrote his Antitheses and published his New Testament, the question still needs to be answered whether Marcion intentionally excluded other writings, as Tertullian claims (disallowing Rev., 1-2Tim., Tit.), and thought of his New Testament as a ‘closed’ collection. If, what would need further research, later Marcionites altered and broadened Marcion’s text, we may have to do with a collection that was meant to be ‘specific’ but not ‘fixed’.
As Tertullian begins his own commentary of Marcion’s Gospel with reference to Marcion’s Antitheses which Marcion has added to the second recension, his publication of the Gospel, he had only knowledge of this second recension.
 Tert., Adv. Marc. IV 4,2: ‘Alioquin quam absurdum, ut, si nostrum antiquius probaverimus, Marcionis vero posterius, et nostrum ante videatur falsum quam habuerit de veritate materiam, et Marcionis ante credatur aemulationem a nostro expertum quam et editum.’
 G.M. Hahneman, The Muratorian Fragment (1992), 91.
 See Tert., Adv. Marc. IV 5,2; V 21.
 This differentiation in G.M. Hahneman, The Muratorian Fragment (1992), 91f. (ibid. more about later Marcionites).