I've actually never quite looked into challenging an NCARB score....
...buuut when it comes to the California Supplemental Exam, CAB says that appealing a score will not result in changing the outcome of the score. In other words, a fail is a fail. But that's from the California Architect Board. Not sure if NCARB has the same policy.
yes, retake is the only way. The reason I ask it is not becasue I want to challenge, but everytime I write to NCARB to complain, they bring that 'review" card up. I wonder if the tons of questions they are getting from 5.0 candidates have urged them to start banking on it.