I don't have the numbers, unfortunately, for the U.S. I do know that the way our system needs to work, and does work, in a self-assessing system is that taxpayers are expected to self-assess, CRA is expected to do their job and review the particular aspects of their tax filings. Conversations happen if there's a dispute. Sometimes it goes to court, but in the Canadian context that's very rare. Very rare. They're encouraged to settle because the court system just can't handle any volume.
On May 3rd, 2016. See this statement in context.