Till the times of publication of the Urantia Book, the historical aspects of the life and teachings of Jesus Christ never existed except those given in the Bible or the Apocrypha Books. And there were nothing for the modern day historians to verify these biblical narrations, except that they are recorded in many books and some have originals which had been carbon dated for their probable period of creation.
But when this book got published in the year 1955, the few readers of the book could not have possibly verify those because there existed no known method commonly known to even the most learned people to cross check those dates easily by manual calculations. Moreover, the idea of computers and computer programs were just getting initiated in the minds of the scientists at the time when the Urantia Book got published for the first time.
We would wonder how the author/s could be so meticulous and accurate when he/they wrote this book when it was impossible to back calculate and maintain that kind of an accuracy!
We might even be forced to deduce that the author/s had some personal diary with them with the chronological events recorded accurately.
It now gives the conversion of dates for the Gregorian, Julian and the Hebrew calendars online by just a click. For example, you could enter the date of the Urantia Book that I gave above (9th Jan AD 7) in the Julian calendar and click the convert button to find whether it was indeed a Sunday. Simultaneously you could also get the corresponding dates in the other calendars as well. Isn't it great ?