What do you mean? They knew, at the time that the particle was predicted, that if it did exist it would have to be within a certain range of mass and would have to be the result of particle collisions where decay or exchange cause the particle to be emitted. Saying that it wasn’t known if those tests would work just isn’t true. The tests would only work if their theories were correct. It wasn’t the testing that was the issue. It was the very rare, specific conditions under which the particle could be observed that was the issue. If they were right, the tests would allow them to observe the particle and they knew this when they theorized its existence.
Doesn’t what make it all the same thing? You’re the one that said these beings could be changing things mid-simulation. If the boiling point of water was suddenly changed, we’d be able to tell. If the structure of carbon changed, we’d know. Then you walked that back and said that they’d just stop the simulation if we noticed these things. But they haven’t because you and I are still here discussing that. So the only options left over, if we assume they can make changes, is that either they haven’t done that or the simulation is perfect and so the distinction between a simulation and a real, physical world is a moot point.