Small illegally assisted performance gains may always be a theoretical probability just due to the window of tolerance required to account for the legitimate biological and physiological changes that stem from events such as illness, and adaption to environment factors and training stimulus.

Similar to some people being super-responders to some performance enhancing drugs, different people have different biological responses to other events and it would take quite some time and research of every athlete to plot every response they exhibit to a situation and the variables which could change that same response in a re-trial under different conditions. Which barely even accounts for the fact that new research and studies might reshape or bring to light new knowledge about the way our bodies work. So being able to completely eliminate any sort of safety tolerances currently looks improbable.

The legal side of things doesn't help anti-doping agencies pursue a stricter set of criteria in the short term due to the legal need to go after the most obvious extreme "open-and-shut" cases so that a clear legal precedent and understanding of how the Athlete Passport system works can be established for less "open-and-shut" cases down the line; athletes are obviously often going to challenge convictions as much as possible. Gradually the tolerances present in the Athlete Passport could theoretically be be tightened as CAS and the civil\criminal courts take notice of prior cases, are more familiar with the Athlete Passport, and over time come to trust the system's validity with each mounting successful case much in the same way DNA slowly came to be trusted as pretty solid evidence for convictions.

Ultimately, if nothing else, the Athlete Passport could help, and has so far helped, lower the severity of doping within sport so that the crucial performance related differences between an athlete who is illegally doping and an athlete who is playing by the rules are as low as possible. Everyone would prefer it if cheaters were easily caught and punished for there dishonesty and misdemeanors but if a more level playing field can be achieved by other means it helps reduce the temptation and rewards of doping, lessening the causation.

It is worth remembering that the Athlete Passport is only one aspect of the fight against doping, if an ever growing part of the fight. Even if a violation is not triggered at a Athlete Passport level the data plotted over time could help focus precious resources on more randomly testing, in and\or out of competition, of potential anti-doping violators.

We all want more resources, time and effort dedicated to the fight and wish dopers could be caught sooner and more often and the illegal act eliminated from sport that is for sure. However, in this imperfect world even if you can't catch them all in a timely fashion there is still a worthy fight to be had lessening the advantages these scoundrels get from doing what they illegally do.