Thus locally there is a drop in pressure on the hull at right angles to this surface that failed. That is, here the pressure differential at altitude is greater that the pressure used in the fatigue life test. Fatigue is very sensitive to the pressure range, moreso that to the actual level of stress.
An Extremely informative post, Old Eng.
Would oil canning be an early indication of weakness in this area of dome shaped stress concentration ? I would imagine joggled rivets could be another but then it depends on the stage of failure with ref to the Insp date.
As a Airframe Inspector i have to carry out crown skin inspections but have never come across ref material indicating the possibility of a localised diff
pr causing the scenario you describe.
Cheers.