All of the Monster High items manufactured by Mattel itself have one or two numbers on the back of the packaging, usually in the lower right corner. These numbers are the product numbers, which Mattel assigns to its products — whether they are related to Monster High, Ever After High, or something different altogether — so that they can be systemized. In case of two numbers, the first is the assortment number and the second the model number. In case of only one number, it alone is both. All items that have the same assortment number are part of the same assortment.