A very short answer for a possible very long one: we spent a lot of effort maintaining our airspace database with additional operating attributes like “only at night” or “by notam”. In case of the latter, when EV4 does not find a notam that activates this airspace, it flags it as “most probably not in use”. But it can be EV4 doesn’t find the notam link allthough there is a notam, that is why smartmap only works when notams on map are enabled, so the user still sees the notam circle arround the associated airspace. 

Because we are never 100% totally sure an airspace is not active, we tell so by using “most probably” and the advise to always verify with ATC. 

Btw, the timeframe EV4 uses is either the planned takeoff date/time for a route (in case a route is loaded) or the mapinterest start- and enddates that can be set using that calender button second from the left of the bottombar.