Historic dating systems vary across cultures and continents. Various legendary events have served as milestones of the past. However, there are two primary dating systems that have gained a noteworthy foothold in historic texts.
The first is measured by a historic event known as The Betrayal, when a group of beloved heroes opened a dark gate and allowed enemies to flood the world. Over two centuries have passed since this enigmatic event, and so the current era is measured as Post Betrayal.
(OOG Note: 206 PB is equivalent to 2006. 215 PB is equivalent to 2015)
The second, lesser known dating system was named only a few short decades before the Betrayal, when a horrific necromantic & abyssal plague struck the continent of Lairroth. These times were referred to as the Post Plague Years.