Al Fadi and Dr Jay compare the time between Mohammad's death and the time the sources of Islam (the Sira, Hadith etc.) were written is over two hundred years and 200-300 miles north from the place that was thought.  While the time it took the Christian to write their sources is about 60 years and it was written in the same place where Christ lived and died while eyewitnesses lived.  They say if we compare it to the history of the United states, the biography of George Washington and the constitution would of not been written until the 21 century.