When the user sees data for an old invalid milestone, it is not immediately obvious. For example, look at data for F35 Final:
https://qa.fedoraproject.org/blockerbugs/milestone/35/final/buglist

It is not clear that it's F35. It is not clear that it's no longer updated.

Proposed solution:
If the displayed milestone is not active, show the milestone identification ("Fedora 35 Final") and some visible warning dialog that this milestone is no longer active and the displayed data are outdated. Make sure to display it in all related views (Info, Bug List, Updates).