I like this quote from starfinder page 430.
"On some worlds, however, scholars use the preexisting local calendars for events before the Gap. Those researching the cultures from Golarion, for instance, sometimes uncover documents referring to dates in ar or “Absalom Reckoning,” a measurement believed to have been used for nearly 5 millennia, starting with the ascension of a now-dead and mostly forgotten god of humanity named Aroden."