The New Testament is, in and of itself, an implicit claim that its contents are the writings of Jesus’ apostles (and their immediate associates) – that all the writings of the apostles were included and that none of their writings were excluded. That is, the ancient church is telling us that they gathered all the apostolic writings they could find and called them “the New Testament.”
The modern church can come to a different conclusion from that of the ancient church, but it cannot change the ancient conclusion. The position of the ancients is what it is. Antiquity went to its grave claiming that the New Testament writings are apostolic and that no other writings are. Their verdict has been rendered. Modernity can only accept that verdict or reject it; we cannot change it.
Therefore, the New Testament itself is a prima facie case for apostolic authorship. What it is ostensibly, it is actually.
Related post on a different blog (Bible Study Notes for the Kingdom of God): Individual Writing Apostles