well, here's an old theory of mine.
dunno if you've heard of it before.
Giants can live about 3 times the lifetime of a normal human. And the Void Century occured roughly 800 years before current events in One Piece.
but there are out of the norm humans who can live well past 140 years old. eg Dr. Kureha(and she's quite young) so it's not too unreasonable to assume that there are giants who can live well past their normal expiry date.
why not a 900 year old giant, saavy?
so I theorise that there is a giant on Elbaf, probably a patriarch or a matriarch(who knows, there may be female giants too) who actually lived through the Void Century. An actual living eye witness to the events of the time.
that would probably give Nico Robin an orgasm.
And even if there are no giants that old, The Void Century is only a minimum of 3 generations back. so it's very likely that there are some of written or oral record of the events.
And since its very unlikely that a great warrior country like Elbalf would waste their time with the likes of the World Government, their records if any would be independent and most likely unaltered…