I am not sure what you are referring to as spurious.
Given the range of dates, it is quite possible for Mohammad to have been born, lived and died inside of that range. That in turn, means that the oral traditions could have easily have started prior to the script in question. It also means that the capture of those oral traditions in the form of this script is quite possible. The dates do not NEGATE the Quran as the author attempts to portray.