I find it amazing that the books and manuscripts are still around hundreds if not a thousand years later meanwhile the dye medium of my data CDs from the mid 90s is probably rotten.
"Never been sacked" is important as well. Often books can get burned and destroyed during political upheaval, either intentionally (burn the books) or accidentially (the building with the books goes on fire).
When the Spanish conquered what is now Mexico, they destroyed all the Mayan books. https://en.wikipedia.org/wiki/Maya_codices#Background > "We found a large number of books in these characters and, as they contained nothing in which were not to be seen as superstition and lies of the devil, we burned them all, which they (the Maya) regretted to an amazing degree, and which caused them much affliction."
> Mari holds the key to much of our knowledge of this era. The site of Babylon has physically sunk over the years so that now the palace and archives of Hammurabi are below the water table and, presumably, reduced to mud
> As in the case of Ebla, the vast archive of thousands of documents from eighteenth-century [BC] Mari is preserved because the palace burned down. [...] Because of this, it is possible to read, in some of the letters baked and buried in the conflagration, about Hammurabi's relations with Mari in happier times.
Our documents from that period come from conquering kings who, in their zeal to raze enemy cities, forever preserved those cities' records. Literature wasn't as much of a presence then as it is now (tablets run to accounting and correspondence), but it (and history) existed; cf the epic of Gilgamesh.
The preservation strategy in every age has been data redundancy, but it's much easier to duplicate and copy digital information.
Glad we had all those monks copying the copies of copies so we still have all that ancient philosophy. =)