If I create a Scheduled Reminder for Event feedback, eg 16 hours after, should I expect it to go out to all past events?
We had the same issue - making a new post-event feedback email live via Scheduled Reminders unexpectedly triggered emails to hundreds of past attendees of events from years ago.

Until the issue is fixed, one workaround is to set-up a Smart Group that adds attendees to new events of this type that occur only after a certain date. Then in Scheduled Reminders, use the "Limit to" field to only send out to contacts in this Smart Group.