...and at the end of the day...shipping instructions are just instructions, like the instructions on the side of the road on the maximum speed that no one really looks at.
There are countless ways to make it much harder to ship the wrong part, from simple barcoding to form fit 'nests' in the packing box that another part wont fit into, to (notably an extreme) granting access only to the correct part with no ability to grab something else.
When I worked in a shop making precious metal inks, it took three people to access the ink (the person responsible for the ink, the person responsible for the room in which the ink was, and a supervisory signoff to release the metal...in addition to the shipper.
Instructions may or may not get read...but no one is going to accidentally take something from a locked room when they have no key.
Simple barcodes can create a scream when things don't match (order & product).
Fitted nests can make you pause and ask "Why don't these fit in here right?"
Do humans make mistakes? Constantly. Looking at the system can generate ways to catch or prohibit the mistakes from going out the door...that's why you look at the system instead of the person. One can be "fixed"...the other can't.
Assigning blame to a person doesn't typically help the company. Looking for a solution in the system to prevent recurrence (or occurrence) CAN help the company.