No matter how many separate eCard invitations you send for an event, your guest list is automatically consolidated for you in your 'invitation list'. Use your invitation list to keep track of who has viewed and responded to your invitations.
You can easily re-send an invitation to guests that don't respond after sending the first round of invitations. If you want to send reminders or any other follow-up information to the people you invited, you can do this from your invitation list. Your 'guest list' is different in that it includes people who have responded to the invitation.