Well Boxtops, I guess that since the ones which make up the New Testament, along with others, were all in circulation around 150 years after he died, they would have been written well after his death.
Then again all those marvellous Old Testament quotes come from documents written well after the events they spoke about too Still as they all relate to the bad stuff people get up to, I guess they tell us far more about god and religion that the gospels do. After all, behaving decently towards the people you meet and deal with as you go through life just doesn't have the same headline grabbing potential as the older stuff