An agent in possession of an advance medical directive vesting any power or authority in him shall, when the instrument is otherwise valid, be deemed to possess the powers and authority granted by such instrument notwithstanding any failure by the declarant to deliver the instrument to him, and persons dealing with such agent shall have no obligation to inquire into the manner or circumstances by which such possession was acquired; provided, however, that nothing herein shall preclude the court from considering such manner or circumstances as relevant factors in a proceeding brought to remove the agent or revoke the directive.