It's not clear how you can assign a candidate a 90% chance of graduation. That probability must be a subjective assessment that has come from some (biased) source. In truth, an individual will either graduate or not.
In your example, you can assign 0% and 100% probabilities in group A, but you can't in group B. The most plausible mathematical explanation for that is that you collected insufficient relevant information about candidates in group B.
It's not clear how you can assign a candidate a 90% chance of graduation. That probability must be a subjective assessment that has come from some (biased) source. In truth, an individual will either graduate or not.
In your example, you can assign 0% and 100% probabilities in group A, but you can't in group B. The most plausible mathematical explanation for that is that you collected insufficient relevant information about candidates in group B.