You'd be surprised.
Many years ago I read an article about "dragon bones" (as the country folk called them). They were actually pieces of turtle shell, written on and then burned by shamans. After the burning they were shattered; the belief was that the pieces could be "read" for fortunes etc. (Like other cultures looking into entrails.) Anyway, modern scientists had no trouble identifying many of the characters - very little change. (Others were completely different, and their meanings long lost.)
Related: Spoken Chinese has several "dialects" that are more like separate languages, but the written language is universal. (I've seen Chinese diners in Chinese restaurants in the US write their orders for the waiters for that reason.)
Don't lose too much sleep over 'lost knowledge'. The Bible claims to go back to the beginning of human history (whether written or oral), is readily available in almost every modern language, and in more of them every year, yet people still steal, kill, envy, etc. etc. In fact, 1 Tim 3:1-5 looks less like prophecy and more like plain news each passing day. ![]()
Back to the Chinese: Look up a guy named Joseph (?) Needham. He wrote several volumes on ancient Chinese technology; firecrackers ain't the half of it.

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