When you sign up for a Pro Twitter Stats account we start recording your Pro Twitter data from that moment. Twitter Counter cannot display statistics for data that was not recorded. However, we try to get as much Pro Stats for your account from Twitter. Unfortunately, Twitter also has to deal with system availability. Which means in some cases we don't get all stats from your account from Twitter.
Good thing is that when it comes to evaluating your account, you can always look at the main trend per month. Even when there are gaps you usually should be able to create a report on a month to month basis.