[Graham]

Maybe a label securely fixed to the box with:

'IF UNDELIVERED - RETURN TO XXXXXXXX'

The problem being that they did not consider the original label at all which did have a Sender and receiver address on it, unless it fell or was torn off I cant see any reason for changing it. So in that case why would they consider any other form of label (which is visible).

I still think that this was probably done for malicious reasons, and if so how could you stop the person from changing ANY visible labels ?

Obviously the original order tracking number was working, because that was used eventually to deliver the parcel from the Lost property Office to Kevin.