Yeah, I thought about that too. But then you can learn a lot from even a null experiment. How you explain it to the taxpayer is another question.
I don’t know how you separate QM from the Standard Model, though. Obviously, the thing that went wrong here was their calculation of the probabilities. That methodology is provided by QM. If you constantly find something else to blame for the failure of the predictions besides QM, then of course you’ll never find fault with QM.
You've got the wrong idea. When I search for "meson production", dozens of paper abstracts pop up, a sampling of the many hundreds written in recent years. Here's one from 1982:
Abstract. Presents a model of cumulative pi --meson production in the interaction of relativistic deuterons with protons. The interaction of three nucleons is calculated by taking two- and three-particle forces into account. The differential cross section calculated for pi --meson production shows good agreement with the experimental data.
It's a complicated business! When discrepancies with experimental data are found, nobody thinks "Uh oh, Quantum Mechanics is wrong!"