When I’m invited to speak for a lunch or other event, I always ask the organizer for the list of expected registrants.
Then, once at the event, I collect the business cards of all the attendees for a door prize drawing of one or more of my books,
plus I request their list of who actually showed up.
Later, back at my office, I compare the Registered and Actual and usually, there are quite a few who didn’t show up.
I contact every one of them. In one case, a while ago, the registrant was a CEO of a big technology company (in Silicon Valley)
who was called out of town at the last minute and couldn’t make the talk. He had bought my book and had been reading it.
He invited me to see him, and after two meetings, we had a huge consulting and training project.
Leave no stone unturned — there could be gold in those no-shows!