Product identifiers look like a small detail in a feed, yet they cause a large share of the warnings and "limited performance" notices that sellers see in Google Merchant Center. Getting GTIN, brand, MPN and identifier_exists right is one of the cheapest ways to improve how often your products are shown. Here is a practical breakdown for Shopify and custom-store sellers.
What counts as a GTIN
A GTIN (Global Trade Item Number) is the barcode number assigned to a product through GS1. In a feed you will usually see one of these formats:
- UPC (12 digits), common in North America
- EAN (13 digits) or EAN-8, common in Europe and Asia
- JAN (8 or 13 digits) in Japan
- ISBN for books
- ITF-14 (14 digits) for multipacks and cases
Google checks the number against GS1 data and against the check digit. Numbers from restricted prefixes (for example the 02, 04 and 2x ranges used for in-store and variable-weight items) or coupon ranges are rejected. Do not invent numbers or buy cheap "barcode packs" that are not registered to your brand: a GTIN that belongs to someone else can produce "mismatched GTIN" or "incorrect identifier" issues, and repeated mismatches undermine trust in the whole account. If you are unsure which attributes are mandatory for your category, review the full list of Google Shopping feed requirements before you change anything.
When you must submit identifiers
For new products that have a manufacturer-assigned GTIN, submit it. Brand is expected for almost all new products (media such as books, music and movies are the main exceptions). MPN is only a fallback when no GTIN exists. If you resell a branded item, use the manufacturer's GTIN exactly as printed on the packaging, not your internal SKU.
When to use identifier_exists = no
identifier_exists tells Google whether your product is supposed to have standard identifiers. Set it to "no" (or false) only when the product genuinely has no GTIN and no brand plus MPN pair, which is typical for:
- Custom-made or made-to-order products
- Handmade and artisan goods
- Vintage items and antiques
- Private-label goods that were never registered with GS1
Using "no" on a product that actually has a GTIN is a mistake that Google can detect, and it usually leads to reduced visibility. Our guide to optimizing Google Merchant Center product data explains how identifiers combine with titles, attributes and images to improve matching.
Shopify-specific tips
In Shopify, the Barcode field on each variant is what the Google & YouTube channel sends as the GTIN, and the Vendor field usually becomes the brand. Common problems we see:
- The barcode field holds the SKU instead of a real GTIN.
- All variants share one barcode, although every size and color needs its own.
- Vendor is set to the supplier name rather than the brand shown on the product.
- Leading zeros are dropped when a CSV is edited in a spreadsheet.
Fix these at the source in Shopify rather than overriding them in Merchant Center, otherwise the next sync will bring the errors back.
Reading the diagnostics
Identifier problems show up as item-level issues such as "Invalid GTIN value", "Missing value [gtin]" or "Limited performance due to missing identifiers". Most are warnings rather than disapprovals, but invalid values can block items entirely. If items are already rejected, work through the checklist in how to fix disapproved products in Google Merchant Center, and for larger catalogs consider a structured approach to Google Shopping feed management with supplemental feeds and rules.
Summary
Use real, registered GTINs; give every variant its own; set identifier_exists to "no" only for genuinely unidentified products; and correct data in your store platform first. Clean identifiers help Google match your listings to the right searches and keep your account in good standing.
If you would like an expert audit of your identifiers and feed, the team at MerchantCenterPro helps Shopify and cross-border sellers fix Google Merchant Center issues.
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