Currently, we have support for (but are not using) a banner for unsupported versions of the docs, that reads:

                f"This version of of {package_name} is no longer supported. "
                "If possible, upgrading to a newer version is recommended."

We've never defined any versions as unsupported, so this has gone unused. We'd like to add a banner that gets applied to all non-latest docs versions, noting that it is not the most recent.