Hi,
don't know about an official document. But.
When trying to download and install upgrade packages via CPUSE: it will not show or download new releases or jumbo HFAs. (I haven't tried it, but the statement should be correct.)
However, an offline upgrade is still technically possible.
If your User Center account still has download entitlement through other devices with valid subscription, you can manually download the upgrade packages (e.g. R82), upload them to the appliance, and install them via CPUSE offline mode. The appliance itself does not block the upgrade based on its own contract status.
Whether this places you in a licensing or support grey area — or even outside what is officially permitted — I can’t say. My explanation was purely from a technical perspective.
and now to something completely different - CCVS, CCAS, CCTE, CCCS, CCSM elite