Actually, that's true for any good item, with some exceptions. A plain heksher (kosher symbol) doesn't mean kosher for pesach even if there are no grains in the finished product. Kosher for pesach certification insures that, in addition to the food being kosher, it was made in a grain free factory, where the machines had been cleaned according to the constraints of religious law before being used to cook kosher for pesach food, and with someone knowledgeable on site to ensure no errors were made in production.

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