Structural damage on the aircraft from the 1997 incident was identified only during the 587 investigation in 2002. Six other planes that were also inspected around that time came out clear. From NTSB Press releases:
Feb 25, 2002:
As a safety precaution, Airbus and American Airlines are removing the vertical stabilizer of that aircraft for non-destructive inspection; Safety Board investigators will be present later this week when the stabilizer undergoes ultrasonic inspection to determine whether the stabilizer sustained any damage during that incident.
Mar 11, 2002:
Investigators report that an indication of damage (possibly delamination) has been found that apparently was not present at the time of manufacture. The indication is at the pin bushing of the right rear lug.
Apr 12, 2002:
In addition, the FAA and Airbus identified seven Airbus A300-600 and A310 aircraft whose vertical stabilizers needed to be ultrasonically inspected because of possible high lateral loads experienced by those aircraft. Three of the aircraft were from American Airlines, and the other four were from FedEx, Tarom and Interflug (two European carriers), and the German air force. The FAA reports that all seven have been checked and only one exhibited any damage to the vertical stabilizer. That was the previously reported American Airlines flight 903 aircraft that experienced an upset event in 1997.
http://www.ntsb.gov/Pressrel/2002/020225.htm
http://www.ntsb.gov/Pressrel/2002/020311.htm
http://www.ntsb.gov/Pressrel/2002/020412b.htm