It seems that setting the world date changes the timeline date abbreviation but only from a point onward. It's not the before 0 or after 0.
There are 3 abbreviations in this order: A.I., A.P. and P.P.
The current era is in the P.P. calendar, but when I set the world date to year 137 P.P. It changes the abbreviation for the A.P. era but not the A.I. era
Setting the Abbreviation in "after year 0" on the world, changes abbreviations even in years before year 0.
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