I'd recommend not using store-bought pumpkin spice blends. Spices lose some of their potency shortly after being ground, so any store-bought spice is going to be less flavorful than its freshly ground counterpart. And when you combine several pre-ground spices into one pumpkin spice blend, the flavor will always be lackluster. On top of that, there’s no way to tell how fresh (or not fresh) the pre-ground spices are when the commercial manufacturer bottles that pumpkin spice blend.