Duplicate submissions still happening

Starting June 28, we have been receiving multiple submissions from the same people for our event "2017 Atlanta Catechist Conference - Marist School Atlanta." Before June 28 it wasn't happening. I asked for help a short time ago and was told to try adding the captcha widget. We did and duplicate submissions are still happening. We can't add the IP address widget to avoid duplicate submissions because we oftentimes have to register people ourselves, so we'd be using the same computer with the same IP address. 

In you settings you can enable the "Unique Submissions" feature. This will prevent multiple submissions.

I see you are not able to do a strict check (based on IP address) because you dont want to block yourself.

But you can do a loose check (cookie based). That will prevent multiple submissions unless the user (or you) empties their cache first. 

Ok. And that won't affect people already registered, correct? Also, any particular reason this didn't start happening until June 28? 

Correct, this will not affect users who have already submitted the form.  If a user needs to submit the form again, all they would need to do is clear their browser cache/cookies.