My opinion is the reason swarm cells begin around the perimeter of the frame is because the queen is laying full speed. She has pushed the edge of the brood to the outside edges of the frame. Swarm cups are built on the edges of the brood where there is room to construct the cell downward.
Supersedure cells are made during a slowdown of laying so the brood area is more centered in the frame.
When the swarm cells are made and used there will be one or two dozen cells, and they will have larvae/pupa of different stages of development in them. Supersedure cells will usually be less than six or eight and they will all be the same stage of development.
When the cells are capped, if the queen is still in the hive it is a supersedure. The queen will depart the hive on the day of, or the day after cells are capped if it is a swarm situation.
Swarming situations usually have very large adult bee populations and many frames of sealed brood, and are usually before or at the beginning of the nectar flow. Supercedure situations are usually at the tail end of the nectar flow, there will be a reduction of frames with brood.
Supersedure can turn into an emergency queen replacement if the queen is injured or sick. She can die earlier than expected, and the bees will begin emergency cells in addition to the supersedure cells started earlier. Learning to judge what the bees intentions are comes with experience (also known as making mistakes).
