Start with the product record
A product name describes the item. A SKU helps your business manage it. A manufacturer identifier helps distinguish a particular manufactured product across systems. Before filling a missing field, determine which identifier you actually possess.
Create a short worksheet for one product and two variants. Record the public URL, internal SKU, brand, manufacturer part number when supplied, and GTIN from a verified product record or packaging. Keep the source beside each value.
Review identifiers without inventing them
Google advises supplying an assigned GTIN accurately and avoiding guesses. Some products have no assigned GTIN. An empty field is a reason to investigate the product record, rather than generate a number. Google Merchant Center's GTIN guidance.
Check these common implementation situations.
- A platform exports an internal SKU into an MPN field without evidence that the manufacturer uses it.
- Different sizes or colors inherit one identifier even though the manufacturer supplied distinct product records.
- A feed integration removes leading zeros from a value stored as text.
- A theme and a schema app emit conflicting identifiers for the same product.
These are review scenarios, rather than findings about your store.
Compare the page with its underlying data
Use the Product Schema Checker to see whether the server response exposes SKU, brand and GTIN/MPN fields in Product JSON-LD. Presence alone does not validate a number or establish which variant it belongs to.
For a custom-branded item, ask the person maintaining the catalog which identifiers are assigned and which sales channels require them. Keep internal inventory codes separate from external product identity in the implementation brief.
What a useful repair ticket includes
Include the affected variant, the current emitted value, the verified source value, the theme or integration that writes it, and a repeatable validation step. Check one unaffected sibling product as well so a template correction does not overwrite valid data elsewhere.
Run the free three-product scan for a bounded first look at public product evidence.