From what @Spencer said the new people are automatically added to the event when the invite/reminder/newsletter goes out. You shouldn’t have to go into each event as it sounds like it will refresh and pull the new members as part of the process of sending out the invite/reminder/newsletter. If in your experience this isn’t working properly then send an e-mail to support@trooptrack.com with some examples and they can take a look and see if there is a bug or something else that might be preventing this from happening correctly.
I had to manually add the person, so she could RSVP in time.
Did you have to manually add them or where they added just by you going into the Details of the event? From what @Spencer said above it should have added them automatically just going into the Details of the event.
I went back into the Event, then unchecked & rechecked “everyone.” Then saved it. Then TT pulled in the new member name.