I am sure what happened is SW discovered they had missed the required inspections and contacted Boeing and maybe the FAA about a 10 day window to catch up that allowed minimal disruption to their schedule. This was approved by Boeing probably since 10 days is a minimal amout of time to extend an inspection period (remember this isn't a switch, the planes don't suddenly get cracks the just because an inspection interval passed). It turns out a small percentage of the planes had cracks that required repair. Obviously cracks the size found are not catastrophic since none of the planes crashed.
As for all the minor problems some have reported with SW planes (seats etc.) any airline has to make decisions every day on when to fix minor problems balancing customer inconvienence of a non-functional item vs inconvienence of cancelling a flight due to aircraft availability.
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