A missing GTIN is not a field to fill with any convenient number. Establish which exact product is being sold and whether a manufacturer identifier exists. Your shop’s internal item number serves a different purpose.

Separate three types of identifier

An item ID distinguishes records in your data source. An item group ID connects suitable variants in a product family. A GTIN is a product identifier that needs a reliable source. Google describes variant grouping through item_group_id and handles missing identifiers separately through identifier_exists.

Choose a small product family and compare the available information:

  • Sold variant: Which colour, size or other option does the customer receive?
  • Internal mapping: Which item ID and family assignment does the export use?
  • Supported identifier: Which details does the manufacturer or supplier confirm?

Do not replace missing data with incorrect data

Fictional example: three shirt sizes inherit the identifier of their parent shop product. Copying it across all variants fills empty fields but does not verify which identifier belongs to which size. Compare the variants against the supplier list before changing the mapping.

Setting identifier_exists to “false” is not a general substitute for researching a missing value either. Its suitability depends on the actual product and Google’s stated conditions. Keep unresolved identifiers in an open list until they can be supported.

Export the corrected family again

After the change, check that each variant keeps a stable item ID and its family assignment remains understandable. Open its landing address too: it needs to match the offered variant. You can reuse the same record when comparing price and availability.

Product data & Merchant Center cleanup limits the work to up to 20 variants and ten agreed fields in one source. Unsupported manufacturer data is not invented. Additional products, delivery countries or ongoing catalogue maintenance require a separate scope.

Technical sources: Google Merchant Center: identifier_exists, Google Merchant Center: item_group_id.