Storied is a new mechanic in The Hobbit, and it works a lot like the City's Blessing. It is a static ability that constantly checks whether you control three or more artifacts, legendaries, or Sagas. The moment you do, you get an enduring story.
It sticks around
Once you have an enduring story, it is yours for the rest of the game. Drop back under three artifacts, legendaries, or Sagas and you keep it anyway.
One story is all you get
Every card that cares about enduring stories looks at the same thing, so you cannot stack up multiple enduring stories. You either have one or you do not. The only way to lose it is to restart the game.
Karrrrrrrrrrrrrrrrrrrrrrrrn!