Yes, it was certified of course; then withdrawn for a few months while very extensive investigation was made of every possible aspect that might have brought down G-ALYP out of Ciampino. Quite a few modifications were made, including electrical and fire safety before it was re-issued.
2 weeks later G-ALYY was lost and the certificate withdrawn indefinitely whilst the largest accident investigation of its kind took place.
It was this investigation that introduced cyclic water-tank testing to establish a safe fatigue life of a/c pressure-hulls.
The original CoA was based on extensive testing of samples and sub-sections of the fuselage.
I think it is a rather trite point you make....