While the limit is indeed bizarrely chosen, I think that one falls into the fairly common case of the FDA setting a per-pill maximum, not a limit on overall qua

While the limit is indeed bizarrely chosen, I think that one falls into the fairly common case of the FDA setting a per-pill maximum, not a limit on overall quantities. There's a limit of 100mg potassium per pill, but afaict there aren't any controls on buying the supplements in bulk, so you could order thousands of the pills if you wanted. The total-quantity limits seem to only be on things where the DEA has gained some authority over the substance.