SANJIESAN LORE / Historical chronology
Anchor two fictional era counts to one shared event
Two characters may describe the same historical event with different year names. World Anvil’s timeline features support organising setting chronology, but the author still needs a deliberate relationship between invented eras. Begin with one shared event and a small comparison rather than filling centuries with dates before the counting rules are clear.
Name the event before its two dates
Choose an original bridge opening or a publicly witnessed journey. Describe it once without an era label, then give the labels used by two communities. Decide whether their year boundaries coincide. A simple constant offset works only under assumptions you have actually chosen; it should not silently cover different year lengths, different starting days or a deliberate reset in one of the systems.
Compare a date on either side
Place one earlier and one later fictional event around the anchor. Work through the labels manually and check their order, especially if there is no year zero or if a system changes its era name. You do not need a sophisticated calendar to do this small exercise. You do need to say when the systems diverge so an apparent contradiction is not dismissed as mysterious local tradition.
Let the reader follow the important comparison
Use both era names in a scene only when the distinction matters. A character might recognise that two apparently separate accounts refer to the bridge opening. Give enough context to follow that recognition without demanding mental arithmetic from every reader. Keep the project chronology as the reference for later scenes; an in-world conversion error can be intentional, but the author should know which statement is mistaken and why.