Dixi, your comments regarding damage tolerance are not entirely accurate. Since the late 1980s it has been recognised that damage tolerance evaluations are, unfortunately, not “good forever”, they do have certain limitations. It may be possible to reevaluate a design to extend its life with a significant amount of additional analysis and testing, supplementary inspections and modifications, and even then the type certificate holder may sooner or later come a point where it is just no longer economical. There has been a lot of regulatory and industry activity to address continuing structural integrity issues, perhaps most prominently the problem of widespread fatigue damage, see regulations such as the FAA aging airplane and WFD rules and the recently amended EASA Part-26, which e.g. stipulate a limit of validity (LOV).
Apologies for the thread drift, but I felt this had to be clarified.