Use a SKU to manage your own inventory, a GTIN to identify a widely manufactured product globally, and an MPN to identify a product within its manufacturer.
The codes can appear beside one another, but they answer different questions. A shopping system may use them to distinguish products, match the same item across sellers, connect variants, or trace a record back to the merchant's catalog.
The safest rule is simple: preserve codes from an authoritative source, keep their types separate, and never invent a GTIN or copy one from a similar product.
What each product code means
A SKU is created by the merchant for stock and operations. A GTIN is a standardized global identifier that may appear as a UPC, EAN, JAN, or ISBN. An MPN is assigned by the manufacturer to distinguish one of its products. A channel item ID is the stable identifier for the submitted record.
One product can legitimately have all four. Keep separate fields so a system does not mistake a local stock code for a global identifier.
- SKU: the merchant's internal stock code
- GTIN: a global code assigned to a trade item
- MPN: the manufacturer's part number
- Item ID: the stable identity of the submitted record
- Group ID: the shared parent identity for related variants
Do not guess a missing identifier
A wrong identifier can connect a listing to another product. That is worse than honestly recording that the value is unavailable. Do not remove digits, pad a number, reuse a parent code for every child, or copy a barcode from a similar colour or size.
If a widely manufactured product has an assigned GTIN, retrieve it from the manufacturer, supplier, packaging, or another authoritative product record. If no GTIN was assigned, follow the target's rules for brand, MPN, and the absence of a GTIN.
Catalog cleanup can normalize a supplied code. It cannot manufacture evidence that an official identifier exists.
Check codes at the option level
A shirt in small blue and the same shirt in large green are separate purchasable options. They may carry different SKUs and GTINs even though they share a product family. The export should preserve the child code and the shared grouping relationship.
Review at least one product with several options. Confirm that each row keeps its own ID, code, price, stock, and attributes after normalization and target conversion.
Build a product-code source of truth
Choose the system that owns each code, document the field mapping, and stop downstream tools from silently rewriting it. Keep the source record ID and extraction time so a disputed value can be traced.
When a value is inferred for internal processing, mark it with the reason and provenance. Eligibility flags, manufacturer identifiers, product claims, and merchant-provided metafields should never be inferred.