Back in late WotLK or early Cataclysm, Sylvanas siezed control over the remaining four Val'kyr, after we had killed LK.
In a questline in Silverpine, we learned that there was only four left, and no chance of more.... EVER..
Yet, during Broken Shores scenario, we clearly see FIVE Val'kyr come flying in..
Where did that last one come from?