Perhaps Libby was not asked the question and therefore, not obligated to answer.
"Perhaps Libby was not asked the question and therefore, not obligated to answer."
Perhaps its the other way around. Libby told about it, Miller didn't. "Now" she discovers the notes.
Sound familiar? Rove said Cooper called about welfare reform. Cooper denied it. Later, he checked his notes and voila, he might have talked about welfare reform.