default probabilities

CFA Level II
#1

Why this statement is NOT correct?

The default probabilities of debts from different borrowers that have the same credit rating will often be different.

I think it should be correct. Credit rating tends to be stable over time. It does not always change as business cycle changes. But default probability changes as business cycle changes. Therefore, different borrowers that have the same credit rating may have different default probability due to the change in business cycle.

#2

If default probabilities of debt with same credit rating are really often different, what is the necessity of credit rating?

So, in my opinion, the right statement must be:

The default probabilities of debts from different borrowers that have the same credit rating will not often be different.

#3

The keyword is often.

Will be same = incorrect

Will be different = incorrect

Will often be same = correct

Will often be different = incorrect