It sounds like they're combing over historical manufacturing records: > The company “conducted a thorough review of the manufacturing data with respect to both

It sounds like they're combing over historical manufacturing records: > The company “conducted a thorough review of the manufacturing data with respect to both shimming and skin surface profile. Based on that analysis we were able to determine that both conditions affected these eight airplanes only,” said the Boeing spokesman, who added that it has notified the Federal Aviation Administration “and are conducting a thorough review into the root cause.” Who knows why they decided to review that data. Maybe they have a project to try to spot problems they missed before, or maybe someone just noticed a problem on a newer plane and they went back to find out if any others were affected by that same problem.