Judging whether any of it worked
Two honest numbers sit on your dashboard: page views and sign-up rate, plus the statuses on the list after the session. That is enough to run a comparison. Change one thing between two dates โ the title, the length, the day of the week, whether reminders were on โ and watch whether the no-show column moves.
What you cannot do is measure attention. There is no engagement score, no verified attendance feed, no per-person report from a platform we do not connect to, and no reason to pretend otherwise. The list plus your own memory of the room is the evidence, which is why marking attended and no-show the same evening is part of this rather than a chore after it.