It’s my understanding that mass produced items are all basically the same. If you buy something like a toothbrush, for example, then any other toothbrush from that same assembly line is going to be basically the same and have all the same specs (with the exception with minor defects here and there), because the machinery and process to make any those toothbrushes are all basically the same.
But that can’t be the case with locks and keys. Because if every lock and key were the same then there’d be no point in having them. Anyone could just bought the same key/lock combo could use it to unlock your front door. So all or most keys and locks must be unique. So how are they mass produced in a way that preserves their uniqueness?
Mass produced items are not all the same. They are merely similar, and can have whatever variations the bulk manufacturing process requires or allows.
Not every car made on the same assembly line on the same day had the same options, and near every cake baked in a mass bakery will have a distinct internal structure.
You can never step in the same river twice!