If you want to launch on the Grand Tour, your launch options are the 1970s and the 2140s.
You hit the date, you test what you can, within that constraint.
(They were also heavily budget limited, and I’m sure everyone here has an example of a project which became more expensive because someone decided they “couldn’t afford testing”).
Even then, even despite people who probably have PhDs in specific engineering topics I can’t even name, half the time you can’t even tell what’s important to test vs “it’s common sense this will work fine for a thousand cycles” — hence the long list of missions which failed catastrophically.
