@lanodan @hannah Wouldn't be surprised
if there are some fairly old phonograph records with audio books on them.
Or magnetic wire spools. Open tape reels. Etc.
But probably no or few full-length books from before the 1930s or so.

I stumbled on some ancient 78-RPM records as a kid in the 1980s. These were
thick and heavy. Like, the size of a standard 33 and 1/3 RPM record,
but the thickness and weight of a glass dinner plate. One was from 1901,
and it had a few minutes of comedy recorded on it.

Assuming the media are properly preserved, you still need the technology
to play them.

In the late 20th century, audiobooks for the blind were typically made
in special formats. In the US: 4-track cassette at 15/16 inches per
second (half of standard speed), phonograph records at 8 RPM. The 4-track
meant separate recording on each of the two stereo tracks of a side of a tape.
One track would be recorded forward and the other reversed. With a computer,
a standard tape deck, and the sox utility, anyone can decode these things.

After the rise of Audible, all bets are off. Unless someone pirates an
audiobook and strips the DRM, no way will anyone be able to decode those
at some unspecified point in the future. One good reason to pirate all the
things. DRM is an attack against culture akin to book burning.