Message Performance Report vs. Email Message Response Summary Report

Can someone explain what exactly is the difference between "Actions Taken" in the Message Performance Report and "Advocacy Responses" in the Email Message Response Summary Report?

I'm trying to find out exactly how many email recipients took action on the advocacy page that was linked to in the message but seemingly every report I run gives me a different number. I'm aware that the Message Performance Report only runs every 4 hours for only 7 days after the message was launched. But what criteria is it using to determine "Actions Taken"? I'm also aware that the Email Message Response Summary Report returns every action that was taken by an email recipient while their session was active, even if it wasn't the one linked to from the email message. However, removing those actions that were not linked to from the message does not give me the same number was the "Actions Taken" in the Message Performance Report.

Also, I've exported all of the Interactions where the Interaction Subject is the action alert in the email and the Interaction Source Text is the name of the Email, but that gives me a different number from the above reports.

I'd really appreciate it if someone could explain why these numbers don't match up.

Thanks!