Lookup record from table that may or may not have a match

Yeah automation makes sense.  Could you provide some screenshots of your tables?  How are the attendees selecting the opt in?  

Assuming you have a Participation table where each record represents a single Person and a link to an Event, you could create a lookup field to grab their Opt In details:

And if you were using an Airtable form for this you could then use that lookup field to customize whether the ‘Opt In’ checkbox field is visible in the field or not.  Not really sure if this would work for you though, and if you could provide more details on your workflow I’ll see what I can do to help!

Sure, here are a couple of screenshots that include the relevant data. I load the data from another Airtable base with a simple copy and paste. The participants use a Fillout form to opt-in and create the record in the Opt-in table. That’s all working fine. But now I would like to make a modification and have a master opt-in table so that participants don’t have to opt-in if they have already done so at a previous event. But that means some participants will have matches and others won't. Also there will be records in the Opt-in table that won’t have matches with participants. I’m not sure if that would be a new table or just modify the existing Opt-in table… The NACSW number is unique to each handler (participant). 

I appreciate any suggestions you have on how best to manage this process. I don’t want to have to manually link the records if I can avoid it. 

Hmm, do you have a table where each record is a single NACSW number?  If not, try creating a new table with that data, and the quick way to populate it would be to:

1. Create the new table called ‘NACSW #’ or something
2. In ‘Entries’, create a linked field to NACSW #
3. Click the field header of the field ‘NACSW Number’, which will select the entire column
   1. Do this in a view where no records are hidden
4. Hit CMD / CTRL + C to copy
5. Click the field header of the field ‘NACSW #’, i.e. the linked field
6. Hit CMD / CTRL + V to paste
7. This will create one record per unique NACSW number, regardless of how many Entry records may have that unique number

In the table NACSW #, create a lookup field that’ll display from entries that indicates whether the person has opted in before, and then create a view to filter those out.  You should now have a list of all the people who haven’t opted in yet that you can reach out to, does that help?

Thank you. I’ll take a look at this when I get a chance and let you know if I have any questions.