[yldedly]

Yes, it's correct to say that I have knowledge of your conjecture, and in the same way that physicists have knowledge of QM and GR regardless of their truth status, but beyond just having knowledge of the theory, they also have knowledge of the reality that the theory describes.

>Were NASA physicists indefensible to use Newtonian mechanics to send a person to the moon because Newtonian mechanics are "wrong"?

No, it was defensible, and that's exactly my point. Even though they didn't believe in the content of the theory (and ignoring the fact that they know a better theory), they do have knowledge of reality through it.

I don't think instrumentalism makes sense for reasons unrelated to this discussion. A scientist can hold instrumentalist views without being a worse scientist for it, it's a philosophical position. Basically, I think it's bad metaphysics. If you refuse to believe that the objects described by a well-established theory really exist, but you don't have any concrete experiment that falsifies it or a better theory, then to me it seems like sheer refusal to accept reality. I think people find instrumentalism appealing because they expect that any theory could be replaced by a new one that could turn out very different, and then they see it as foolish to have believed the old one, so they straight up refuse to believe or care what any theory says about reality. But you always believe something, whether you are aware of it or not, and the question is whether your beliefs are supported by evidence and logic.