item_id should always match your Product Catalog and system rules to maintain Eureka's quality, functionality, and analytics. Mismatches in the item_id can lead to several issues that directly impact your business outcomes and the user experience. For example, analytics on products, such as purchases, cannot be matched with the feed.
Analytics are based on the item_id collected from system rules and passed to the hit. If this item_id does not match the XML item_id, you will have ghost products in the feed that were updated from the XML without any analytics.
To resolve these issues, you should update your XML feed so that the item_id aligns with Insider's system rules. Once updated, the analytics for your products will correctly attribute to the products from the XML feed and drive meaningful insights.