You think they are sent exactly 1 code for every GPU they order? Guess you never worked anywhere that had promotional codes
usually there's so many staff can have one each
It's not part of the product either and I would argue less so than any instructions or the box the gpu came inside.
Ok lets stop thinking of it as just the "product" and more as an SKU, the card and the code will form one SKU it's this you return under the DSR.
Either way I think there's a high chance OcUK will sort this with very little drama.