If you over-type or edit into an old email campaign and then resend it - the report stats will add these new email campaign stats to the old so the report information will be meaningless.
Always duplicate an old email campaign by clicking on the Duplicate icon as shown below:
Once you have duplicated a previous email campaign this creates a new campaign which you will see at the top of your e-Marketing campaigns list.
Please rename and edit the this duplicate email template as this will not have any report stats associated with it.
Please be careful not to edit the second email campaign down or one underneath the first listed duplicate as this is the original and will have the report statistics associated to the old campaign.