AFAIK for items shipped by Amazon the only way to rule out commingling is after delivery: If the barcode starts with an X that's an FNSKU (specific to a seller), meaning the item did not come from commingled stock. Items sold by Amazon itself never start with an X, so...
Yeah, I guess that doesn't mean anything but marketing, it still all comes from the same place.
The OP article doesn't discuss this, but it seems to me a likely explanation for someone getting crap levi's ordered on amazon?