The problem has only been observed on undelivered fuselages, because those are the ones that Spirit has on-hand to check. They are not confident the problem is absent in delivered aircraft.
You could also say, "the problem affects all of the delivered aircraft that have been checked for the problem".
From another article:
> As of Friday, the "non-conformance" or quality defect had been found in 22 fuselages out of 47 inspected up to that point, spread between Boeing and Spirit, and may exist in some 737s in service, the sources said.
The problem has only been observed on undelivered fuselages, because those are the ones that Spirit has on-hand to check. They are not confident the problem is absent in delivered aircraft.
You could also say, "the problem affects all of the delivered aircraft that have been checked for the problem".
From another article:
> As of Friday, the "non-conformance" or quality defect had been found in 22 fuselages out of 47 inspected up to that point, spread between Boeing and Spirit, and may exist in some 737s in service, the sources said.
https://ca.finance.yahoo.com/news/exclusive-boeing-delays-73...