BR:

Let's go one work at a time. Josephus. Yes, alteration COULD mean what you suggest, but the point does not apply to the logic for Josephus having said something given a later reference to James and Christ later in the book which has no textual doubt surrounding it and assumes some remark earlier. Josephus is still first century and lived in the area of Jesus' ministry; so this is important evidence. In other words, it is quite likely that alterations did take place (as I and many others who have studied the text accept). The changes took place from Christian scribes who altered a part of the text to make it say more than it originally did). This situation of soem alteration is more likely than the alternative that the entire citation is inserted, which cannot explain as well the assumptions that the later reference suggests.

The other later texts. Their dates alone do not matter in and of themselves Alos important is the potential line of transmission and tradition. We would have to doubt and question a great deal of what we understand about earlier classical history if we had to say a source centuries later for an event cannot count. Sources have to be weighed, not merely dated. If a late first century or second century source has a line back to the early years (as say Clement might or Polycarp through Ignatius who knew John) then we may well be able to work our way back. In 2007, I know some things about WW 2 (over 60 years earlier) because a woman who lived in our house was the wife of a man who was in the German army. She would tell me stories when I was a child about what life was like in Germany during the war, stories I still recall. Even more than that, she was able to tell my children the same kind of story so if my children live to be 70, then one can span over a hundred years and still be in touch with an eyewitness. So the chain of transmission is as important as mere dates.

dlb