The story of Oakwood is vast and multifaceted. And long. Very long. Every so often, a major event comes along and alters the world so much that a new timeline must be invented to properly pay respects to the change that has occurred. The first of these events is the Great Storm. Although it's difficult to pinpoint exactly when the AD time period ended, scholars in the subsequent AS Timeline never recovered anything written or recorded after 2063. They generally agreed this was the year when the storm finally overwhelmed humanity and rebooted history.
All but four of the chapters revealed so far take place in the AD Timeline. "Thirsty," "Hungry," and The Secret of El Sol are all set in 000 AS or shortly thereafter. "The Scout" takes place at some point during the SQ! Timeline.