I have started randomly adding new starsystems and stellar clouds to empty subsectors. These empty subsectors are in totally empty sectors. The bottom line is that, although it is likely that an empty sector you already scanned will remain the same, it is not guaranteed. I have no idea who has scanned a sector or if it has been scanned at all so you might want to start doing some extra sector probes to see if anything is different. I will be adding stars for several weeks if not months.
Have a great weekend!