It may help to check who is the actual seller, as Amazon these days is as much a distribution center for third parties as a first first party retailer.
I've heard conflicting reports on whether Amazon co-mingles its own stuff with third party sellers, but some people have certainly claimed so. What co-mingling (it's opt-in for sellers) means is that Amazon doesn't distinguish which FBA seller gave them a particular item and will ship out the one that is cheapest to ship to that particular customer. Think of it as a giant distributed pile, where every seller's Koss Porta Pro end up. Now if I order one and the warehouse closest to me has units that a different seller handed to Amazon, I might get one of those, because co-mingling means that they're treated as identical. Remember that this is opt-in on the seller's part, and it's not entirely clear to me whether (or under which circumstances) Amazon co-mingles its own stock.
Yes, I'm pretty sure that that's the case with the fake Koss Porta Pros (headphones). If you're going to make and sell a forgery, why would the barcode be a problem? Barcode or no, passing off the forgery as the real deal isn't exactly legal.
I don't see the point of making a fake but refraining from forging the barcode.