buttman writes:

As far as in-between could layers, its only reported by pireps. Its
very common to ask ATC what the cloud tops are and get a response "I
don't know, no one has given any pireps yet" No one hardly ever flies
VFR between cloud layers, because its too easy to get stuck, therefore
no one bothers making a chart for multiple cloud layers.

That hadn't occurred to me. If you're VFR you definitely wouldn't want to be
stuck between clouds, so the in-between layers aren't important. And if
you're IFR it doesn't matter ... unless the clouds are associated with icing
or severe turbulence.