Daniel's view of the Judgment Seat of Christ.

        While the Thrones were placed (ready for those who should be found worthy to occupy them) they were not yet occupied.
                   Their occupancy had to wait for the outcome of the judgment.

Now as the Thrones that John saw were occupied by crowned Elders. Those Elders must have passed the fiery test of the Judgment of Reward and recieved their crowns.
1 Corinthians 3:11-15
2 Corinthians 5:10