As often happens in this forum, I think a lot of the disagreement boils down to semantics. Regardless of whether the word “shift” is incorporated into the rules, it’s obvious that a shifting process has occurred during the case, when first one side, then the other, has had the ball thrown into it’s court (as Gasquet would say). De facto shifting, if you like.
What I find interesting, and a little disturbing, is that, as Python notes, Bert was considered to have met his initial burden. Why, indeed, is a transfusion theory required? Given the negative test immediately preceding the positive, everyone has to accept that Bert did not take CB knowingly and intentionally in anything remotely approaching an effective dose during the Tour. So he certainly has a right to ask WADA to propose some other way CB got into his system. But given how remote the possibility of contamination is, and given that Bert has provided no evidence that indicates that this very remote possibility would not apply to him, why should WADA have to prove anything more than transfusion is possible? To most people, even including scientists speaking precisely, one in a million is not possible. So anything possible trumps it.
Everyone will agree that transfusion, including the two step version, is possible in the physical sense—means exist for withdrawing blood, separating cells from plasma, storing the components in a way that accounts for DEHP in one and CB in the other, and re-infusing at a later time. It’s also possible in the practical sense, in that the various steps could actually be accomplished by a rider at various times before and during the season without necessarily failing a test or being caught in the act. There can be arguments about how probable this is, including how likely it is Bert would actually transfuse, how likely he would use the techniques required to account for the appearance of two different substances at different times in his system, and how likely it is his blood manipulations would not be detected. But does anyone seriously equate these probabilities with the one in a million chance of contaminated meat?
The fact that the case has come to this—let alone if Bert walks—shows very clearly that a lot of people, probably including the arbs in this case, do not believe the CB statistics. No one can possibly claim that the transfusion theory, two steps or not, has a probability of occurring of no better than around one in a million. If you are really sceptical, maybe one in a hundred, but nothing remotely approaching one in a million.
So when this case is finally settled, particularly if Bert walks, I hope someone intimately involved in it will explain how they came to believe that the CB statistics are not reliable. There is some other factor, not explicitly acknowledged, that leads people to conclude that the possibility of contaminated meat is many orders of magnitude greater than the stats indicate. Maybe they believe there is a lot of corruption in the system, that a lot of meat, particularly imported meat, dodges the controls. Maybe they believe the region where Bert's meat came from is a local hotspot with a history of cheating that was missed by the testers. Or maybe they just don't believe the testing system is reliable at all. I really hope, though very much doubt, that the arbs confront this issue head on, and provide some sort of estimate of how likely contamination is, and why.