Oh by the way, defective units are handled a different way for stores.
When I worked for BestBuy, if a product stopped working within 3 months, they got a brand new one right off the shelf. This defective unit would be sent back and we wouldn't get a refurb, we'd get a brand new one in its place.
So, given this context, it's also possible that rather than receiving a refurb not included in shipped numbers, the stores with special warranty and return policies could be receiving shipped units in place of the refurb. This scenario is even better for both companies, and business-wise more likely.
MS would be able to repackage the repaired console as a new one, and gamestop would keep the warranty costs. This would also explain why Gamestop eventually stopped selling warranties because as quality improved it took longer to fail, if it fell outside the defective unit grace period, they'd start receiving refurbs, and probably started building quite a large stockpile.
Evidence that supports this is that within one month or so, you could still return the item if it became defective. Also, warranties were pulled in its third year.
