As in most cases of the kind, the productive period soon ceased, and the later writers had a choice of two things, either to harmonise the conflicting records of previous historians, or to develope their details in the manner that we find in the Apocryphal Gospels.
But if Justin used a single and separate document or any set of documents independent of the canonical, then we may say with confidence that that document or set of documents belonged entirely to this secondary stage.

It possesses both the marks of secondary formation.

Such details as are added to the previous evangelical tradition are just of that character which we find in the Apocryphal Gospels.

But these details are comparatively slight and insignificant; the main tendency of Justin's Gospel (supposing it to be a separate composition) was harmonistic.

The writer can hardly have been ignorant of our Canonical Gospels; he certainly had access, if not to them, yet to the sources, both general and special, from which they are taken.
He not only drew from the main body of the evangelical tradition, but also from those particular and individual strains which appear in the first and third Synoptics.