The NT books commonly agreed on by all Christians in the first century were..
The Four Gospels
Acts
All the letters of Paul except Hebrews (uncertain authorship, I believe he did write it)
1 Peter
1 John
And that was all.
200 years later additional books added were...
James
2nd Peter
More private letters of John,
Jude
Revelation.
Even then there was enough doubt about them that they were placed together in the back of the Bible.
My pastor's cousin is doing his PhD work on the authorship of Hebrews. He is arguing that LUKE wrote Hebrews down as a sort of dictation based on a sermon from Paul.
To me it makes sense ... Hebrews sounds Pauline ... but looks Lucian.
Just a theory ... but one that doesn't cost anything ... lol
Cant wait to read the thesis.
Researchers at MIT and the Smithsonian who have used a plethora of methods, analysis and so on to fix the 4 Gospels in the first century show that 2nd Peter, 1 2 and 3 John and others were apparently not written in the first century but were in the Johannian school of thought and one in line with Peter’s thought in the second century - the same for Jude and some others, too.