How do I get Retrospective feedback for an event using a Webform (participant Custom Data)?
OK - I have it,
for this I've set up a Scheduled Job that fires off to &quot;attended&quot; participants a few days after the event. I set up a smart group of &quot;participants whos participatory date was after [a month ago]&quot; so i didn't spam older participants, and used the group as an &quot;include&quot; filter.
Set up an event, of the right type, so that it would get fired.
Added contacts to the event (and gave them the &quot;Attended&quot; status.
Created the webform and including (from the CiviCRM tab):

existing contact
firstname
lastname
contact ID
checksum

then in the &quot;Event Registration&quot; section

show past events: all
Registration Options &gt; Disable unregistering participants: yes
Registration Options &gt; Allow events populated from URL: yes
under Contact1
no of event sets for contact1: 1
event(s): User Select
&amp; any needed participant custom fields

and build the checksummed url:

http://example.com/node/xxx?event1={event.event_id}&amp;cid={contact.contact_id}&amp;checksum={contact.checksum}

think that's it.
let me know if I missed a bit (or did anything stupid!) and I'll correct it.