↑The New Essential Chronology states that the Ruusan Reformation occurred in 1000 BBY, which is the zero point of the calendar based on the Ruusan Reformation, so the difference between the calendar based on the Battle of Yavin and the Ruusan Reformation's year-notation system is 1,000 years. This date is derived using simple math based upon other confirmed dates.
↑The Essential Atlas places the Battle of Yavin, the zero point in the Galactic Standard Calendar, in 35:3 under the Great ReSynchronization dating system. The Essential Atlas also places the Battle of Selaggis on 43:2:28 and the Battle of Dathomir on 43:3:21. The Essential Guide to Warfare and The Essential Atlas both place the Battle of Dathomir in 8 ABY. The Essential Guide to Warfare also places the Battle of Selaggis in 7 ABY, confirming the placement of the division between each Galactic Standard Calendar year as the third month in the Great ReSynchronization year. Thus, there is a two-month gap between the two dating systems, and the first two months of a GrS year are the last two of the preceding Galactic Standard Calendar year. The Great ReSynchronization was instituted in 35 BBY, so there is a total difference of 35 years and 2 months between the two systems. This article's date is therefore derived from simple math based on this reference explanation.
↑Andur Sunrider leaves H'ratth for Ambria in 4,000 BBY per Tales of the Jedi 3: The Saga of Nomi Sunrider, Part 1. The Tales of the Jedi Companion says that 2 years prior (4,002 BBY), Andur went to H'ratth, and six years prior to that (4,008 BBY), he saw the Force ghost of his grandfather Jev, who the Companion says disappeared on a mission a year prior to that (4,009 BBY). If you start at 4,000 and count back the number of years (2, then 6, then 1) you arrive at 4,009 BBY, which has to be the year of Jev's death, given that he appeared to Andur in ghost form a year later (4,008 BBY).