Hello,
EA/CG does not give a year long schedule. Usually we only get a calendar month by month around the end of the month, and those are subject to change. I have been playing this game for 2 years and double drops are rare, but there is a pattern to them. We will usually get double drops at or around May 4th, Anniversary or the game/Winter holidays, and when a character(s) is needed for a special event like Phoenix for Thrawn. Hope this helps.