Obviously, when a white or black raven comes into play, the season begins. It remains so for the time in which they are in play. But what happens when they are discarded? Does the season remain? Or does the season go away when the initiating card does?
Complicating matters are the Crowns--Winter, Mereen, Azor Ahai. The text on those makes plain that the Ravens supercede them, but what about each other? If I have the Crown of Mereen in play and later my opponent marshals the Crown of Winter, what season is it? What if I have the Crown of Winter in play but it is then discarded? What happens then?
And finally, how do you know this stuff? There isn't FAQ listings for all strange interactions; is there a compendium somewhere that can be searched? There's lots of questions like this that can come up....
The key to figuring it out is if a card says a thing happens that effect only works while that card is in play unless the card says otherwise (and it will almost always last for the phase when it does say otherwise).