From the USPS Domestic Mail Manual, section 170,
subsection 4.1(i):
"Computer-readable media containing prerecorded information and guides or
scripts prepared solely for use with such media."
I've asked and our postmaster has said anything that's not blank is OK (we ship a
lot of diskettes!). I'm sure interpretation is basically arbitrary when it comes down
to stuff like, "how do we classify these disks from the 70s that someone is
inexplicably writing new data to in 2022?"
Thanks,
Jonathan