Natural Soap gets its cleaning power from the development of glycerin during the saponification process. This is different from conventional mass produced soaps which use chemical surfactants and added glycerin. 
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Natural Soap has a shorter shelf life than soaps with chemical surfactants. It's made to be used. The shelf life depends on the quality of care, that it be kept in a dry spot out of direct sunlight, and the amount of unsaponifiable constituents left over in the soap after saponification. Unsaponifiable constituents help to protect the skin from being stripped by the soaping action of the bars. So it's a balancing act to produce a soap which has longevity, and is also protective of the dermis. I lean on the side of a more protective soap which has a shorter shelf life. Soap which has gone off has a slightly fishy smell, though doesn't stop being soap. An off soap may show orange spots where  caustic oils have congealed.
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Natural Soap can develop Soda Ash which is a soft white ash on the surface. This is also from the saponification process and does not affect the quality of the soap. It simply washes away with the first couple of uses.
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Natural soap is naturally fragrance neutral, with the saponification process destroying most naturally occurring essential oils in things like herbal infusions. This is why mass produced and vanity soaps rely on perfumes and essential oils. We don't use any added fragrances or fragrance enhancers. 
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My intention is to give you the closest thing to an apothecary made true soap!