This 14:49 video discusses the oral tradition about Jesus which preceded, and was the basis for, the written texts we have in the New Testament.
Excerpt (14:14 through 14:35):
Scholars estimate the reliability of an oral tradition can last for over a century before we could expect corruption to seep in. Gilbert Garraghan says it cannot go past 150 years (A Guide to Historial Method, p. 259-262). Marelene Ciklamini sets the limit at 200 years (Old Norse Epic and Historical Tradition, p. 21). This is well within the time frame of when the New Testament was written down even if we take the latest dates for when the books were written.