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." 
  On Wed, 12 Oct 2022,
Jonathan Chapman via cctalk wrote:
  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?" 
Not blank is certainly a more reasonable definition than the cockamamy
"only if it was written by a publisher" silliness.
'course, an FORMATTED disk, without any "user" content is not
"blank" :-)
--
Grumpy Ol' Fred                     cisin(a)xenosoft.com