SE's support page has this little line of information:

If you participated in Open Beta phase two, the client you already have installed will be sufficient, and you can skip the following step. If you participated in Open Beta phase two, but have since deleted the game client, you can re-download the game by visiting the “Library” menu on the PlayStation®4 home screen.
Perhaps it's intentional that our codes are marked as used already if we were part of open beta?