On the way out, confirming the time for the appointment to have the permanent crown fitted, I mentioned the page. The mystery cleared: the page was for the next appointment, because the new automated system they've installed sends text messages 14 and 3 days before each appointment. Looking more closely at the text, I realized that it was indeed for June 30, not June 17. The receptionist said she's going to ask the service to stop sending 14-day messages anyway.
Now that the anathestic has worn off, my jaw feels very sore. Still, my dentist did the best he could under the circumstances. He's a very good dentist, but some things are unavoidable, and keeping your mouth open that long for all of that grinding is not easy.