how does their calendar work?
Can't be like ours, because ours is based on revolutions around the sun. Their seasons are unpredictable, so they must have a different method. And they must have one, or there wouldn't be "name days" and such.
shareI have read all of the books several times and I really cannot tell you for for sure.
Generally, the years are based upon a set number of days and are not tied to the seasons in any way.