I don't know if this is accurate. The earliest gospels date back to decades after Christ died. If men alive at the time who knew enough to remember it were still knocking around later around the time that the author of Luke was writing then they would have been pretty old, I think.The New Testament was written by men who were either eyewitnesses themselves, or who related from the eyewitnesses their personal accounts of the actual incidents and teachings of Christ. It is beyond doubt that the New Testament accounts of Christ were circulated within the lifetimes of those who witnessed his life. It is also a fact that these people (some friendly, others hostile to the gospel) would confirm or deny the accuracy of the accounts. The bitter opponents of Jesus and his disciples would have leapt at the opportunity to discredit the claims concerning his life, death and resurrection, if the writings being circulated were untrue.
I'll have to do some research. I'm going by memory. I know Luke was first (and it had the fewest miracles and no claim that Jesus was God). The others came later and they each added more and more layers of total nonsense like miracles and such. That's how mythology grows.