Nothing has apparently been reported yet about the level of CB detected. Studies have shown that, yes, a lot of Mexican meat is “contaminated”, meaning it wouldn’t pass EU inspection, but even so, much of that contaminated meat would not produce the level of CB found in Bert (50 ng/ml)—which really was not that high.
Keep in mind that it took a highly sensitive apparatus to finger Bert. A more typical detection limit is around 100-200 ng/ml, and even that is far below the minimum detection limit required. To test at 200 ng/ml, you have to eat meat contaminated at a level that seems to be pretty uncommon even in Mexico. Still, we are talking about maybe 1-10%, odds far better than what Bert faces in Spain. To test at the minimum detection limit of 2 ug/ml you would have to eat meat so contaminated that you might start worrying about a public health problem. So the actual level of CB detected could be quite relevant to their prospects of being cleared.
Beyond that, I think for these players to get off, they need to establish: 1) they all ate meat from the same source; and 2) (if possible) there was no one else who ate this meat who did not test positive.