Reporting Discrepancy

We have deployed a few email campaigns and have a few questions. With the two emails campaigns we have sent, when we click email link performance and check on the leads, the number of leads in the email link performance tab does not match the leads on the dashboard page (the one you see after you deploy the email) Does anyone know why that is? And for reporting purposes, which figure should we actually revert to, the one from the email performance tab or the figure showing up on the dashboard? Is there any difference between the leads that are being pulled from the dashboard than the ones that are under the email link performance tab?