Meaning that either there's another unaccounted variable(s) that controls the effect of A in B and C, meaning that we cannot conclude anything from the experiment.
Yes and no is not acceptable...
All the people who use this law do so because their work is about some kind of model, which can be wholly known. However, if you have a misfortune of working in the real world - like nearly everyone - then you can't apply this law. This means that you won't ever get a proof in a mathematical sense. You won't ever be completely certain - you can be convinced beyond reasonable doubt, but that's all.
So when we talk about how biologists are just grant hunters because someone couldn't reproduce their experiments we need to take this into account. I don't know, but if I had to guess I'd say that nobody ever expected these experiments to be 100% accurate, 100% reproducible or 100% true. I think they are treated as a data point, some input to think of, and not definite truth.
But I may be completely wrong here, of course.
It is not "reproducible" yet it is incredibly valuable.
Not every work of science needs to be exact fact before being published. Really, nothing in science is accepted as absolute fact. The scientific publishing process is a conversation between scientists to try to determine the truth.