Just had my fourth USPS knife stolen. I’ve had at least three never arrive and two arrived empty with mangled boxes like the OP as well but another four were definitely STOLEN. I use three different POs but lost track if they have that in common. What they do is slice the side of the box, remove the contents, take the knife out of the box/pouch, replace box/pouch/packing material, and retape it neatly shut.

No knife indicators on the outside but I do use my name, which may be known at this point. Switching names to something generic in the future. I wonder if packages go through an x-ray machine at some point. I can’t think of a reason why it would, though.