https://www.amazonsellers.attorney/blog/pros-and-cons-of-ama....
> In summary, Amazon's commingling inventory can have serious implications for FBA sellers who are wrongfully accused of selling defective or inauthentic products. While the practice may improve efficiency, it can also make it difficult for sellers to prove their innocence in the event of false accusations. Sellers should be aware of these risks and take steps to protect themselves, such as opting out of commingling inventory or closely monitoring their inventory and customer feedback.
To your point, maybe it depends on the product?
https://sellercentral.amazon.com/help/hub/reference/external...
> By default, we use the manufacturer barcode to track eligible inventory throughout the fulfillment process, unless you change your barcode setting or your product is not eligible. When more than one seller has inventory with the same manufacturer barcode, we may fulfill orders with the inventory that’s closest to the buyer, to facilitate faster delivery.
> If your product isn’t eligible for virtual tracking with the manufacturer barcode, an Amazon barcode is required. You may be able to get an exemption to use the manufacturer barcode by enrolling your ASIN in Amazon Brand Registry. To learn more about virtual tracking and see product eligibility requirements, go to,Using manufacturer barcodes with FBA virtual tracking.
https://sellercentral.amazon.com/help/hub/reference/external...
> By default, we use the manufacturer barcode to track eligible inventory throughout the fulfillment process, unless you change your barcode setting or your product is not eligible. When more than one seller has inventory with the same manufacturer barcode, we may fulfill orders with the inventory that’s closest to the buyer, to facilitate faster delivery