vm-myVM-private is the qube’s private volume.
The two private-NUMBERS-back are copies of the previous states of the
private volume. They are automagically generated for you, and you can
use qvm-volume to revert to one of them - see man qvm-volume in
dom0.
By default two previous revisions are kept, but you can increase or
decrease this as you will, by changing the value of revisions to keep
using qvm-volume.
Template based qubes only have “private” volumes - standalones and
templates have both private and root volumes stored.
I never presume to speak for the Qubes team.
When I comment in the Forum I speak for myself.