TS:yes, I have heard and read many theories about "the orthodox corruption of Scripture".
The problem I have with them is that there are so many crucial things missing from the
acknowledged epistles of Paul:
*Paul invokes no dominical command to go out and preach to the nations. If Jesus had
given such a command, Paul would have surely used it to support his gentile mission,
but he does not. And if Paul's writings were "corrupted" to a great degree by the centralized
church, I believe we would find such a "command" among his writings.
*Paul never invokes the teachings of Jesus in order to support his own teachings about
setting aside the primacy of the law, how people are justified by faith apart from works
of the law. This also became a central pillar of orthodox Christian theology, and if the
letters of Paul had been extensively tampered with by the later church, I believe we would
also have at least one forged attribution of antinomian teachings made by Paul to the
*Atonement theology is also not placed on the lips of Jesus in the acknowledged letters of
Paul. While the cross became the center of Paul's theology, and an undoubted cornerstone
of the later church, we find no reference from Jesus to the atoning significance of his own
death anywhere in the Pauline corpus.
It is the things that are missing, the central planks of the Christian platform, that should
caution us about embracing the notion that the letters of Paul, or the Gospels, were
extensively edited and interpolated by the later church.
First, there was no "centralised church" in the 1st & 2nd century. Interpolations were most likely made by individual copist, either on their own, or under order from their boss, on a item they personally considered important. For this reason, these interpolations were not systematic on every facets of theology or Christology. And when the time would come for others to make new copies, the source manuscript the most complete would be selected, rather than another one with "missing" verses (therefore suspected of deletions), if known. That would explain why, for some interpolations made early, they appear in all the ancient manuscripts we know of, but for other interpolations (such as Mk 16:9-20), they do not show in all these ancient manuscripts.
Second, it was understood Paul knew (well) the heavenly Jesus, through visions and revelations, through the Holy Spirit, through the mind of Christ, etc. (as he said himself in his epistles) but not from the past human Jesus. Paul's gospel did not come from eyewitnesses but from Jesus by revelations (Gal 1:11-12).
So it was not expected Paul would transmit teachings and instructions from the earthly Jesus (especially when Paul had more up-to-date info from above!).
*The heritage of all Israel, the Torah, prohibited adding or subtracting from the laws
But on other ancient scriptures, that necessarily did not apply. For example, very few scholars think the whole book of Isaiah was written by a same author, especially the second part, which looks like additions, made beyond the life span of Isaiah.
*The Essenes were sworn to pass on their doctrines exactly as they had received them
(Josephus "Judean War" 22.214.171.124)
*The Rabbi Hillel was remembered for declaring that "it is a man's duty to state (a tradition)
in his teacher's words"(Gerhardsson "Memory And Manuscript" p.131).
*Paul warned his congregations:"Nothing beyond what is written.."(1Cor 4:6)
Well, that can be said but not necessarily applied.
Paul, for example, did, with addition, some cut and paste on OT verses (http://historical-jesus.info/19.html
), as also did "Mark" (1:2-3). "Luke" & "Matthew" modified, added and deleted on gMark and Q wording, etc.