I would look for further evidence that other products were stored in the wrong location and also assess how much of a risk this presented in the wrong product being delivered to the customer before deciding whether to raise a non-conformance or not.
Now, a simple corrective action may be all that is warranted - rather than a full implementation of a bar code system (unless that is the customer's expectation). Did they run out of room in the designated area? Was product moved without updating location? If you do not avoid that, it can only get worse. As a warehouse function (and they only have a few key functions) I would not minimize the problem.
, not 8.3 Control of Nonconforming Product
.
.