Parcel service code mismatch: what to check before reprinting labels

We had a run of parcels leaving with the wrong service level. The label looked valid, the barcode scanned, and the customer paid for expedited shipping. The carrier manifest showed ground service. Reprinting labels without finding the source would have hidden the problem for one batch and repeated it the next day. I traced it from the order management system to WMS and then to the carrier API…