im assuming it means your official change date is 16th September? if so it means they have caught up. if not are you already on an extention and when was your change date, (it will help gauge how far along they are).
my guess is as with many big organisations the letter is an automatic one its not taken into account regions and current circumstances, if not today i think Scotland and Wales are only a few days away from easing restrictions for the likes of showrooms.