That's just a poorly designed system. The proper natural key is an order number (possibly an alias to an internal ID that isn't shared, like a GUID). The fail

That's just a poorly designed system. The proper natural key is an order number (possibly an alias to an internal ID that isn't shared, like a GUID). The failure mode without blame might be a pickup which contains both orders, in distinct bags. I think most places staple a receipt to the outside of the bag, so that should make this even less likely.