[ceejayoz]

The next sentence of your last paragraph says:

> Sellers are able to choose whether to share identical inventory or not.

That seems to indicate physical commingling. IIRC, avoiding commingling has an additional cost to the seller.

[AnssiH]

As far as I understand it, that just means that sellers have the option to opt in/out of the commingling program (Settings => Fulfillment by Amazon => FBA Product Barcode Preference).

Yes, there is a cost for the seller if opting out - they need to apply their own barcodes to the products in that case.