Just look at that second link I provided: Justin isn't quoting from a text that we know, his quotes predominantly are partially Matthew, then Luke - and hardly ever Markan or Johannine
They are "verbatim enough" for sure, but never verbatim - it would seem that he just makes it all up as he goes, and the later someone uses his material to actually create the text that he is allegedly quoting.
But really, why the hell doesn't he quote his own text, or at least refer to it? And if he is using a non Marcionite text that preceded both Marcion and himself, then how come it is so very similar if not identical to the Luke and Matthew - but never either one of them - that we know?
We can hardly ever exclude anything, Giuseppe, but the likelihood of it all is infinitely small