It looks like all four ran, although I only received 3 of the 4 emails. I also created a single sequence event that ran successfully.
I suspect that the farm events are failing because I modified the sequences associated with the regimens after the events were created. That might explain why they stopped working at different times, as I worked on them over several days.
Since I can’t create a new farm event that begins in the past I won’t be add the existing regimens back to the calendar once I delete the current events. I’ll post an update once I’ve created the new events.