Aha! That’s the ticket! (No pun originally intended.) Thanks, Jennifer.
When I take steps as you describe (actually Edit Event > Break from Series rather than Events > Break from Series), it works just as I would expect. I generally tend to avoid using the WordPress admin bar; I was editing everything from the WordPress interface (when logged in as an admin). From there, I was selecting Events > Events (from the menu at the left), then editing a series or an individual ticket from the Events list. To split a performance from a series, I was selecting the Edit Single link as shown in the image that I am hopefully attaching.
I suspect that the intent of the Edit Single link is the same as the Break from Series command you pointed me to and that this is a deprecated or forgotten method of breaking from a series that should be updated or just eliminated.
For now, I’m a happy camper, and I can do what I need with much less pain given your insight.
Thanks again.