I have a small doubt, nothing major but something I am curious about. How was time accounted before Aegon I? Surely they didn’t use X years BC

From the WOIAF, it seems like they used a system of years since a major event – so years since the Pact, or years since the Old Night, or years since the Andal Invasion, or years since the Doom – and then scholars later adjusted everything to BC/AC after the Conquest.