I understand the point you are making and it is a good point, they can't be certain. I'm not certain. How can anyone be certain?
If I've understood you correctly you are suggesting that they feel able to say Sky are not doping because they are going to rig the testing procedures somehow to ensure that Sky never test positive.
However, that strategy, if such a one existed, did not work for Armstrong, the UCI and by implication the ASO. It didn't matter that he never tested positive, the truth came out in ways beyond the UCI/ASO's control.
* slight point of order: I was using the phrase 'Armstrong never tested positive' to illustrate the above point, and how his ability, with the UCI's help, to cheat tests didn't keep him safe. He did test positive. Also , he didn't make a mockery of the tests singlehandly, he had the help of pretty much the entire peloton.
Not trying to score points here, and would genuinely be interested in if I've understood your point correctly and if so, whether you can accept mine.
@Benotti, read the above, I think it answers your post.