Hathrox III was the site of a biochemical civil war. One army unleashed a plague, believing it has a foolproof antivirus. However, the disease wiped out the entire population of the planet and caused the planet to still be listed as a standing hazard during the time of the New Republic. (Approximate date)
↑The New Essential Chronology states that the Ruusan Reformation occurred in 1,000 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.