No sweat, just a basic misunderstanding.

We design to a 4 G _yiield_ limit.

This is where the wing, after being stressed, no longer
returns to the original shape
It has reached the "plastic" limit and has deformed.
Yes, it has failed, but it did not break.

The 1.5 G safety factor then gives a 6 G _ultimate_ limit.
THIS is where the wing breaks.

mo better?

Richard