"We have learned from none others the plan of our salvation, than from those through whom the gospel has come down to us, which they did at one time proclaim in public, and, at a later period, by the will of God, handed down to us in the Scriptures, to be the ground and pillar of our faith." [Alexander Roberts and James Donaldson, editors, Ante-Nicene Fathers (Peabody: Hendriksen, 1995) Vol. 1, Irenaeus, “Against Heresies” 3.1.1, p. 414.]
That passage does not say that the Apostolic Tradition is entirely contained in the Scripture. It says that God gave us the scripture — true — and that it is the foundation of our faith. Foundation by definition means that something is built on top of it.