You left out the most important point - ASADA must prove an individual used TB4, not just a group of players.
My point is that is not actually required. Don't listen to those who keep setting the bar very high.
IF, and this is the critical point, IF the tribunal is satisfied that player X took part in the supplements scheme and IF the tribunal is satisfied that TB4 was used in that supplements scheme, they can be satisfied that player X used TB4. They do not have to prove on an individual basis that each player had used TB4. That would raise the level of proof required to 'beyond reasonable doubt' and that is far higher than the actual level required.
Comfortable satisfaction is much easier to achieve than some on here would have you believe.
The Tribunal hearings are individualised and if a player wished to make case for not being part of any doping scheme, he could introduce evidence there to exclude himself, assuming he didn't already do so that the SCN stage.