What percent of breaches by outsiders are not detected by organizations?

Business Insider shows two of Mary Meeker's slides on cyber security. Two data points have me wondering how many breaches by outsiders are actually detected by companies themselves.

In the first slide Meeker states that more than 20% of breaches come from insiders, so less than 80% of breaches are from outsiders.

In the second slide Meeker states that companies didn't detect 69% of breaches themselves but were notified by outsiders.

How do we put those two numbers together? I'm guessing that most of the 69% of breach notifications by outside organizations are not notifying the companies about breaches by the companies' insiders. So if there were 100 breaches, of which 80 were by outsiders, and 69 of those breaches were not detected by the company but by outside organizations, does that mean 86% of breaches by outsiders go undetected by companies?

And what about unknown breaches. Meeker's statistics assume that the total number of breaches are known. The 69% of breach notifications are by outside organizations statistic is really saying 69% of known breaches were not detected by the companies. We have no idea how many breaches are not detected by both the company and outsiders.

It is quite possible that organizations are not able to detect 90% or more of breaches by outsiders. 69% is at best a lower bound.