“For this reason, we consider it safe to continue using a given base distribution in dom0 even after it has reached end-of-life (EOL).”
So one could use old Versions of Qubes in production provided the templates of debian and fedora get updated to newer versions.
Only as long as the Qubes OS project actively backports the essential security patches for dom0 in that particular release. That is as long as that (older) version of Qubes OS is supported.
Which is, as you can see from the page already linked, 6 months after a
new release.
I never presume to speak for the Qubes team.
When I comment in the Forum I speak for myself.