Can you rely on the barcodes your supplier prints?

Cartons from a supplier arrive with barcodes already printed, and it is tempting to scan them and carry on. Most of the time that works. Sometimes it does not, and the failures are quiet: the scan beeps, the number looks right, and the stock lands on the wrong product. A few minutes of checking at receiving can prevent weeks of confusion later.

Four things that go wrong

1. One code for several products. The supplier prints the model's code on every colour or size.
2. Several codes for one product. Different production batches or factories use different codes.
3. A code that is not valid: the wrong length, a wrong check digit, or leading zeros lost when the supplier's list was opened in Excel.
4. The wrong level. The carton carries the code of the single piece, or the inner pack and the outer carton share one code.

Add one more: reprinted cartons whose label does not match what is inside.

A spot check at receiving

For each SKU in a shipment, or a sample of them if the shipment is very large:

1. Scan the barcode on the piece and on the carton.
2. Compare both with the packing list and with your item master.
3. Open one carton and check the contents against the label.
4. Write down the result: OK, mismatch or no barcode.
5. For every mismatch, decide before shelving whether to add your own label or to ask the supplier, and photograph the carton label as evidence for any conversation with the supplier.

This takes minutes per SKU and happens before the goods are on the shelf, when a fix is cheapest.

Check that the number itself is valid

Most retail barcodes (EAN-13) end with a check digit, the thirteenth digit, which is calculated from the first twelve. The rule: add the digits in odd positions of the first twelve, add the digits in even positions and multiply the sum by 3, add the two results together, and the check digit is whatever brings the total up to the next multiple of 10.

Take an invented code, 690123456789. The odd positions give 6 + 0 + 2 + 4 + 6 + 8 = 26. The even positions give 9 + 1 + 3 + 5 + 7 + 9 = 34, and 34 × 3 = 102. The total is 128, the next multiple of ten is 130, so the check digit is 2. The code 6901234567892 is valid, while 6901234567893 is not. In Excel this is a short formula, and one extra column can flag every invalid code in a list. Store barcodes as text, or Excel will drop leading zeros.

When a code fails the check

• If the code is valid and belongs to one SKU only, use it and record "source: supplier".
• If several variants share it, add your own internal label for each variant and keep the supplier's code as an alias in the mapping table. Put your label next to the supplier's, and cover the old one only if it is clearly wrong.
• If one product has several codes, record all of them as aliases of one SKU.
• If the code is not valid, treat the item as having no barcode.

An example with numbers

Suppose a shipment has 40 SKUs and the team opens one carton for each. For three SKUs, two colours share one barcode, and for two more the code on the carton fails the check digit. These five SKUs get internal labels before shelving. Without the check, the first count would show a surplus in one colour and a shortage in the other for the three SKUs, which add up to zero and are therefore easy to overlook, and the two invalid codes would not scan into the system at all.

Agree it with the supplier in advance

Ask for the barcode list together with the order confirmation. Ask for one code per variant, and for photos of the carton labels before shipping. State in the order specification that barcodes must be unique for each variant. This will not remove every problem, but it moves most of them from your shelves to the supplier's side.

InventoryHub builds a code mapping table that links supplier, marketplace and book codes, puts internal labels on items without a reliable code, and lists any mismatches for you to confirm before quantities are compared.