Something is puzzling me. A process close to the event horizon "slows down" from the point of view of an observer farther away. If it is every close, it is "running" so slowly that for observers far away it becomes almost frozen in time. If this is what is happening to matter just outside black hole event horizons, then actual black holes have not actually been accumulating new material within their event horizons, from our point of view? We cannot, even in principle, actually observe black holes accumulating mass and increasing their SR?