[JimSEA]

So much of the media for writing can not survive time. Only in the desert would papyrus survive. Luckily the Chinese left cast bronze and turtle shells with records of their written language. How many civilizations wrote on wooden slats or banana leaves or some such in a humid climate? It would explain the "sudden" appearance of writing in many locales.

[SunkenCiv]

I wholeheartedly agree, even those civs which have left inscriptions and whatnot in durable media probably had most of their archives and libraries and ancient versions of the Post-It™ vanish, taking the bulk of what might have been learned into oblivion. Tamil books were written on palm leaves, and the oldest surviving versions of those are about 1000 years old. Elizabethan England used parchment strips (about 1 x 3 feet were the leaves) bound as books, and thousands of those survive -- but they have been carefully preserved. And that is only from four hundred years ago. No doubt many more of the originals went in the Fire of London. From quite near our own time, I'm sure we've all gone to estate sales and garage sales and have seen what were the family portraits and other family pictures about to enter oblivion, and possibly to end up as vintage greeting cards.