They won't look for this information, and he's not entitled to a lot of it. He's trying to flex what little muscle he has, but Monster will either sue him or they won't. They won't give him this stuff.
You think Monster’s lawyers will stop their billable hours for this matter based on this one letter?
But if they take him to court, he could demand that it be produced, show a notarized copy of the letter to a judge and get the judge to agree. Then Monster would be screwed.