Related: Distinguishing Historical from Theological Claims in New Testament Formation
The ancient verdict on New Testament authorship is that the authors of the 27 texts were named in the book’s titles. Whether those men held the stylus by themselves or had help is beside the point. To repeat, the source – that is, the individual responsible – for each text is the person named in each book’s title.
Modern man does not need to re-invent the wheel because ancient men have done this for us. Likewise, we do not to figure out who wrote the New Testament books because ancient men have told us.
The first definition Merriam-Webster gives for “verdict” is “a position arrived at after consideration.”
This ancient verdict was not rendered in unison. On the contrary, the contents of the New Testament were finalized over the 4th and 5th centuries. This is because the Christian movement in its first one thousand years was comprised of geographically-dispersed and organizationally-independent congregations. That is, churches had a single controlling authority only at the municipal or regional level.