This is a wording used frequently for results of experiments: it doesn't state ultimate facts, it states observations - scientists are very careful in stating these. Of course for all practical uses, that means the effects could be observed because they simply were there.
This isn't quite so obvious in optics, relativistic physics, quantum physics etc. - often effects observed do not correspond to neutral facts; you can see an ilusory image, which doesn't mean the image exists, it's just an abstraction, or you observe a particle at location X, but due to relativistic effects it's already at location Y at the moment of observation. Experiments report observations. It's then up to the theory to match them up with predicted facts.
Of course in plain old material mechanics, while the language remains the same, observing some effect means that effect happens for real, no mysteries of universe there.
...and just in case this isn't clear: No, it does not mean "futile observations were performed." - you observe a defect that exists. If there is none, you would at best see "None observed".