I believe the balance of evidence is that the New Testament we have is a fairly close approximation of what existed in the first century, particularly for the teachings of Jesus. Some of the weakly attested stories, like the virgin birth and walking on water, are probably later embellishments and hyperbole.
The corroborating sources are: late first century/early second century bishops who quoted Mathew, Luke, Mark, and Paul's epistles. Bishop Po!ycarp seems to have been a disciple of the apostle John, and could have interrogated him on what he saw. Fragments of John and Matthew dating to the mid second century track with the extant Medieval manuscripts quite well.
Any single one of these corroborating source is not sufficient evidence, but taken as a whole, the existing manuscript evidence is fairly convincing.
Agreed.