Most of the time, you have only one instance of a given mediator and view component.
When you need multiplicity, you must give each mediator to have a unique name. When you have multiple instances of a Mediator registered, you usually pass a value in the type property of the Notification that the each Mediator instance looks at to determine if the note is for them or not.
Have a look at the HelloFlash demo; the HelloSprite and HelloSpriteMediator, and SpriteDataProxy. http://trac.puremvc.org/Demo_AS3_Flash_HelloFlash