Hello, I’ve been trying to solve the following problem with little success:

I have 2 separate surveys for an event; one that people can complete before the event (about what they expect and their demographics) and one they can complete after (about their experience and their demographics). They don’t HAVE to complete both surveys, but may choose to do so.

Both use anonymous links, with a query string that attaches users’ unique IDs to their responses (they both have an embedded data called unique_id which is set from the URL). 

I want to make the second survey shorter for respondents who already completed the first one, so they don’t have to answer the same questions (e.g. demographics) twice.

Is there a way to only display a question to a respondent who did NOT answer my first survey?

I have tried setting up a trigger to add respondents of the first survey to a contact list (with their unique ID as the external reference), but there is no “display to respondents NOT in list XYZ” / “hide if in list XYZ” option that I know of, and the authenticator doesn’t quite do what I’m looking for here. 

Also, I can’t manually import the unique IDs and set it to “display if unique_id is not X” because the event is reoccurring and so I get new responses to the first survey all the time.

Hope this made sense - thanks in advance for the help!