Public attendee lists are a privacy mess
You should not get a directory of 20,000 strangers from an arena night. What you want is the people you already know — or will know — who also logged it.
Radar shows friends on the gig when they have the same show. That is overlap, not surveillance.
Shared counts on profiles
Friend profiles can show how many shows you have in common. That number is more useful than another follower graph.
Tag people in your crew on the night. Future you will not remember who was on the guest list.
If they are not on Radar yet
Send them the download link after the gig, not during the set. The overlap only appears once they log the same date.
Until then, your diary still holds the night. The social layer is optional; the timestamp is not.