Correct. Nagasaki was in the top 15, excluded from the top 5 reportedly at Truman's request. The second intended target was Kokura, and weather prevented several attempts. At what was proved to be literally the last minute, Kokura was abandoned and the backup of Nagasaki was given one attempt, which was successful. Bockscar lost two engines during its emergency landing in Okinawa, its fuel was so low. So Nagasaki was only promoted to backup site because it was en route from a top 5 site.