You will be able to generate a report for the number of followers and accounts that are following you from the moment we started tracking your account. Information about when we started tracking your account can be viewed from your profile page when logged in. You can as well view it from your Buy Stats page. 

Your new follower and unfollower data is gathered from the time you start a free trial or buy a premium plan.    

If you want to get a deeper overview of what data we have please check this article: How far back are the statistics going?