AFAIK they have always segregated different FNSKUs to separate bins for comingled inventory.
The reason you get counterfeit goods is that Amazon prefers to fulfill an order from warehouse A but seller 1 only has units in warehouse B. Seller 2 has units in warehouse A so Amazon performs an item swap between the sellers to save on shipping (or to improve shipping speed).
The reason you get counterfeit goods is that Amazon prefers to fulfill an order from warehouse A but seller 1 only has units in warehouse B. Seller 2 has units in warehouse A so Amazon performs an item swap between the sellers to save on shipping (or to improve shipping speed).