To be precise, it means there may be an update available. The updater doesn’t know, because update checking hasn’t occurred recently, where “recently” is a user-configurable time value.
I don’t see how you arrive at that conclusion.
“Yes” — We know there are updates available.
“Maybe” — We haven’t checked recently, so we don’t know whether there are updates available.
“No” — We checked recently, and there no updates available.
So, of course “maybe” should sometimes become “no” (when you check after a while, and there are still no updates available), and sometimes “no” should become “yes” (when you check again, and now there are updates available). It would be unreliable if this were not the behavior.
I don’t see how this part is any different than any other OS. If anything, Windows seems less reliable than Qubes on this point.
See here: