If the manufacturing for the 2.4 meter mirrors existed a decade earlier, and Hubble used the existing processes, does that mean all the KH-11 satellites also have the spherical aberration problem that Hubble has?
Perkin-Elmer designed a new null corrector to verify that the mirror was made to spec, but the null corrector was incorrectly assembled (one of the lenses was out by a few mm). They also used the previous null corrector to test, which showed that the mirror was incorrectly ground, but decided that the new null corrector's measurements was correct.
The test equipment is a much smaller part of the cost than developing, building and testing the machines required to actually grind the mirrors to spec in the first place.
but that's an awesome rabbit hole you pointed out!