My brother the archaelogical archivist of ancient (~2000 years BCE) mesopotamian artifacts has a lot to say about archival formats. His raw material is mostly fired clay tablets. Those archives keep working, partially, even if broken. That's good, because many of them are in fact broken when found.
But their ordering and other metadata about where they were found is written in archaeologists' notebooks, and many of those notebooks are now over a century old. Paper deteriorates. If a lost flake of paper from a page in the notebook rendered the whole notebook useless, that would be a disastrous outcome for that archive.
A decade ago I suggested digitizing the notebooks and storing the bits on CD-ROMs. He laughed, saying "we don't know enough about the long-term viability of CD-ROMs and their readers."
Now, when they get around it it, they're digitizing the notebooks and storing them on PDFs on backed-up RAID10 volumes. But they're also printing them on acid-free paper and putting them with the originals in the vaults where they store old books.
My point: planning for centuries long archiving is difficult. Formats with redundancy, at least with forward error correction codes, are very helpful. Formats that can be rendered useless by a few bit-flips, not so much.