[NYer]

What do they go on to prove the Greek copy written 1000 years AFTER the time the original was supposed to have been written is an accurate copy?

This question is best answered by Kolokotronis.

[Kolokotronis]

You know, it never occurred to me to question the authenticity of what we call the Didache beyond the obvious understanding that copyists often made mistakes, though far fewer than translators. The Bible used in the West is a classic example of that.

The Didache we read today is in fact consistent with the quotes from it and principles cited by the Fathers going back at least to St. Irenaeus of Lyon which is a pretty good indication of the accuracy of our copy. At base, though, I suppose we accept it because, like the OT and the NT, The Church does.