> put a prominent note at the top of each page "This is an unsupported version of the docs, for the latest version see blah blah blah" and link to the most recent version.


Not sure how straightforward it will be to do this, and whether it will worth the trouble. Julien, perhaps you know more about this and can provide assessment. Perhaps it needs to be done from within python-docs-theme?

FWIW, the landing page of each version (example https://docs.python.org/3.3/) states when it was last built. It can be an indication that it is outdated.

There's also a related issue in python.org to better inform people of which Python versions are still maintained or not: https://github.com/python/pythondotorg/issues/1302

I think as it stands, this ticket is "not a bug".