> If the experiment does nothing to advance this theory over any competitor, or vice versa, how can you say that it provides experimental support to the theory?

Non-contradiction of existing theories can be seen as a prerequisite for support. As a restricted affirmation of non-wrongness perhaps.

>restricted affirmation of non-wrongness

I think this is a really good way to put it, and an important criteria given the timescale over which these theories develop.

You seem to suggest that support for a theory is meaningless unless it is absolutely conclusive. If that was the case, I'm pretty sure most of quantum physics would have been abandoned long ago.

Until we know everything, is anything in theoretical physics really a zero-sum game?

I think the problem is in the thinking quantum physicists must possess in order to believe in such a theory in the first place. I mean, the idea of, "if we don't know where it came from, it couldn't possibly be hidden information; it must therefor be 'random'" is absurdly egotistic in the first place.

I have no idea how you get from my words to, "...support for a theory is meaningless unless it is absolutely conclusive."

What I said is that if the outcome of an experiment is predicted by two different theories, getting the expected result does nothing to help you decide between them. It happens to be the case that ANY experiment that is in accord with quantum mechanics is equally well explained by EVERY interpretation of quantum mechanics. The result is that most working physicists so not consider wondering about the right interpretation to be a useful scientific endeavor. Indeed most will gladly affirm that they belong to the "shut up and calculate" school of physics in practice.

There are plenty of detailed questions within quantum mechanics which can be asked and answered by experiment. That is what scientists tend to do instead of debating interpretations.