I have spent several years in the university, studying History of Ideas and Science and I have learnt that “scholars” at least in the western world agree on one point. This is that a bishop from Alexandria had a mayor influence over what was to be considered as “canonic” letters. This bishop was Athanastasious, well known as the creator of the trinity dogma. This was after a big battle with the Arians, who couldn´t accept that God was three….
Athanstasious have left letters (still stored at the Vatican library) telling all the early congs. in Asia and Italy, which written material, that could be considered as “canonic” . You also must know that during this time there was a numerous different letters circling around in all those first established congs. In fact We have almost noting of the original letters so all of these later letters must be based pure on oral tradition (They are all based on transcriptions of translations of transcriptons …….!!!)
If you want to know more of the origin of the “canonic” scriptures I strongly recommend you to look up prof. Barth Ehrman on YouTube. You can listen to his lessons there and get much information only from that…..
Bugbear