Hi Claire,
Thanks for following up with this.
The only thing I can think of that would give some control over the number of instances for a recurring event is the Create recurring events in advance for setting you can find by navigating to your WP Admin > Events > Settings > General tab.
You can determine how far in advance recurring events will be created. Of course, this is not per event but a global setting for all recurring events, but it will at least give you some control over them.
I hope that helps. Let me know if any follow up questions 🙂
Best,
Victor