Chance that the seller is the spec. Material without notice. Until the lot is the raw material used in production, which affect the quality of the product.
The thing is that the seller has to change the Spec. raw materials without notice until a Lot of raw materials are used in manufacturing, which impacts the quality of the product.
there happened to be that the seller has to change Spec. raw materials without notice until there is a raw material used in the production to the Lot, which impact on product quality.