Supersedure cells look like swarm cells.
Supersedure is where the colony replaces an old or damaged queen with a young one, usually without any brood break. Naturally this happens in the U.K. towards the end of the active season from early August-late September. There are usually 1-3 queen cells built and to give you an idea my saying is "usually one, often two and occasionally three", any more than that and they are likely to be swarm cells.
In my experience supersedure cells can be built anywhere, not always on the face of combs as is often said. Very often they will be on the periphery of the broodnest and I have often seen them on frames, or combs of food where there is no brood. This doesn't make sense to me, but it may be the reason so many are missed. There is a view that workers put the eggs in the cell cups, but I think it is likely to be the queen who lays them, although as ever, I will retain an open mind (useful things they are!).
Supersedure cells, if more than one, are usually within a short distance the same age and not always on the same frame as is often stated.
With the current queen problems it is very common to see supersedure cells in the summer, where the colony has a young queen who appears to be laying well. This is not natural - I started seeing it around the turn of the 21st century and have been trying to highlight it ever since. If you see supersedure cells in these circumstances then my advice is to clip the queen and reduce the queen cells to one, otherwise you are likely to have the colony swarm with the fertile queen. Cutting all the queen cells out usually results in a failed or "disappeared" queen a few weeks later.
It is quite common for colonies to build supersedure cells in a colony where a queen has recently been introduced, especially if direct from a mini-nuc. I don't think this is likely to be a genuine problem, just that the queen may not be up to speed and the bees think there is a problem with her. The cutting out of these cells will usually result in the colony settling down.
If more than one supersedure cell is left in a colony in the summer there is likely to be a swarm, whether the queen is clipped or not, but this very rarely happens with natural supersedure that takes place later in the season, so there is no need to remove any queen cells, although you may wish to use one to produce another queen if the colony is a good one.