Hi Chad, thanks for your help.
I actually have selected this as I have added my Leads all along, but they never showed up in the "Contacts" tab, until now. I didn't change a single thing, I just loaded it today and they showed up. I'm wondering if I hit 'refresh' or something similar that may have reprocessed things? I'm not entirely confident that the list will update in real time as I add new contacts because of this, do you have any ideas why this might be? I will keep an eye on it moving forward, hopefully I'll have a reliable and consistent way to build a Campaign Contact list to review and go back through.