I think that something has changed in the feature that lets you resend an email to new subscribers (or subscribers who it has not been previously sent to). For instance I sent an email yesterday and got a half dozen or so new subscribers today who I would like to send it to.
According to your documentation, it will only be sent to people who it wasn't already sent to, but I would feel more confident if I could see the number of subscribers the system expects to be sending it to. I believe that in the past (before the most recent changes to your interface), that total it was being sent to would show up after you set up the lists. I would really like to be able to know how many subscribers it is being sent to before I click "SEND".