I recall reading that towards the end of the operational
"life" of the P-51 Mustang, the military put G limits on
the airplane that were more restrictive than the factory
originally specified (forget just what the new limit was....).

Point being, the military realized the airframes were
getting old/tired, and did the prudent thing by limiting
the G loads on the poor ole' gals.

It would be foolish to think one could operate an aircraft
up to the design structural limit forever....

Bela P. Havasreti