They ALL knew on Election Day.  The December letter was a formal reminder.  Nothing personal.  Business.  No matter when the notice was given, there would have been complaints that it was at the wrong time:  During Thanksgiving?  No!  Early December?  Don't rush us!  Christmas?  You ruined our holiday!  After Christmas?  You should have told us sooner, because we haven't been paying attention and just didn't know!