Age of Kaien Calendar

Structural lore — what Oda has confirmed about this. Mysteries (unsolved questions) live in Vault/Threads/; this is what the world IS.

What we know

Ch. 287 (page 4): The 400-years-ago Jaya flashback caption reads “May 21, 1122, the Age of Kaien” — the first on-page fixing of the in-world calendar era used for Mont Blanc Noland’s expedition.
Ch. 228: The same calendar (“Kaien”) appears in Noland’s surviving logbook entry, “Kaien 1120, June 21,” read aloud over the feast at Cricket’s island.
Establishes that the Noland era is dated ~400 years before the present in a named calendar system.

Kaien 1120, June 21 — Noland’s logbook entry (Ch. 228); he sailed from “the lively town of Vira.”
Kaien 1122, May 21 — Noland’s expedition lands on the surface-world Jaya (Ch. 287); first contact with the Shandians.

The Noland Legend and the City of Gold — how does the Kaien calendar map to the present-day calendar / the Void Century? (Open; the calendar is canonically real, but its alignment to modern dating is unstated.)

Characters connected: Mont Blanc Noland
Foreshadowing seeds about this topic: Noland Kills The Serpent-God Kashigami To Save The Sacrifice
Predictions that depend on this lore:

Reconcile flag: no prior calendar/era note existed under a different title (verified before creating); this records the calendar as canonically real.