You can adjust the "Sent Date" under the "Setup" tab to each month you would like. You can then clone the report so there is one for each month.
Do you know of any report that shows who has access to MSI? My CRM guy is having problems tracking down who has access based on our complicated profiles. Not all of the people with access use MSI so the Email Performance Report wouldn't help. I tried to have Marketo tell me but they could only say the total number, not what users had accidental access.