All apostolic teaching contained in the NT? Ridiculous. Two-thirds of the Apostles are hardly even mentioned by name - even in the Gospels and Acts let alone everywhere else!
We can be sure that Thaddeus, for example, and Matthias, were every bit as active as Peter and Paul in spreading the Gospel. Yet not a word is written of what they taught.
Let’s put things in perspective here. James survived for ten to fifteen years after Christ before He was martyred by Herod in 44 AD.
So he taught for a period roughly three to five times as long as Christ’s own ministry of three years. Logically, the records of James’ teachings should then be three to five times as long as any of the Gospels if ALL was recorded.
Remember that’s James alone, and he was the first of the Apostles to die. Imagine how long the written records of St John’s teaching should logically be, given that he outlived Christ by sixty-some years.
Care to make the ridiculous assertion again that all Apostolic teaching is contained in the NT?