Having worked in a factory that made ready meals and sandwiches for the supermarkets, I can categorically state that different quality ingredients ARE used for different supermarkets. We had various "grades" of chicken, mayonnaise, bread, etc for different supermarkets. We used frozen chicken pieces for cheaper brands, such as for petrol stations, and fresh chicken for the premium brands. It was FAR MORE than just different stickers - the whole production line would stop, ingredients removed from the dispensers/containers, and refilled with a different grade before the production line would start again. So, yes, same factory, but VERY different ingredient qualities.