Seeds the structural premise that the True History is a suppressed record across many stones, each tied to a destroyed culture. (Noland’s papers — a dead man’s record — supplied the bell/city detail Robin confirms, layering dialogue-from-dead-character onto the reveal.) The ch275 flashback extends the seed from Shandora-was-built-by-the-Poneglyph-makers (272) to the Shandians are its sworn 800-year guardians (275).
The payoff
Earliest known caller
(unrecorded)
Why this matters
A textbook parallel-arc-structure tell: Oda runs the Void-Century macro-plot’s shape (a recording civilization, a war, a deliberate erasure, a hunted truth) in miniature inside a single arc, years before the macro reveal. The Skypiea reader meets the Void Century’s shape through Shandora before ever meeting its content through Ohara/Egghead.