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Can you tell me whether or not soft seed potatoes will still be able to produce a good crop
Seed potatoes should be reasonably firm if they are healthy. Softness indicates some form of disease. I would take them back to where you bought them and ask for new ones.
By the way, it's very unusual if there is a problem with seed potatoes bought from a reputable supplier. They may well be glad you returned them if there really is a problem.