Bart Ehrman destroys Christianity in under 12 minutes.

[Aractus]

Maybe a 1st century manuscript, if any exist, will shed light on the matter.  Fact is that there are some passages of the New Testament that everyone agrees were not in the original texts (the end of Mark after verse 8, the Johannine comma, the Pericope Adulterae, The Testimonium Flavianum, and some others), which shows that Christian scribes had no qualms about altering historical texts, inspired or not.  In addition, no one disputes the fact that about half the letters of Paul (the Pastoral epistles) were not even written by him; ditto for the epistles of Peter and the three letters of John.

Again, none of that is controversial and the only ones who will disagree are fundamentalists and Orthodox Christians, and other people who simply don't believe in critical scholarship. I would actually strongly disagree with you that those examples show that scribes were, generally speaking, quite willing to make alterations. The Comma Johanneum for example is noty found in any Greek manuscript ever, until the 16th century when it was deliberately inserted into one because of its place within the Vulgate. There are two points to note here, firstly despite the Vulgate including it, no one added it to Greek texts for consistency until one person in the 16th century, someone who was convinced it must have been originally written in the Greek. Not only that, but the Vulgate itself was probably based on some ancient Greek variant that included it - yet it died off. That would suggest to me that Christians even in the early days recognised careless copying and preferred the texts they perceived to be more authentic to the author's autograph.

As I mentioned before though, those examples don't advance Bart's argument that the original wording is "un-knowable". The fact is, yes if you want to know exactly whether the originals said "Christ Jesus" or "Jesus Christ" and how often each version appeared (before the use of the Nomina Sacra which is now found in every single NT Greek manuscript), then you're out of luck. But that doesn't mean you don't know what it said. Whether in Greek appears "Christ Jesus", "Jesus Christ" or the Nomina Sacra variations of CJ/JC makes no difference, you don't need to know which of the two ways it was written down first.

There's a much greater degree of confidence in the original wording of the NT writings than there are of any other ancient Greek text for which the original is lost. Much more than say for Antiquities of the Jews, or any other significant Greek text written in those times - again with the very rare exception of where you might have an original letter.