I believe the second label corresponds just to the violent crime rate. The implied correlation is that leaded gasoline contributes to lead in the blood, which leads to violent crimes 20 years later. i.e. they shifted the line for violent crime to make it overlap instead of being delayed.

I’m trying to tell you that The vampire coalition is blameless in this matter, if only people would believe us. But they don’t. So we are forced to eat them.