I’ve missed two over twenty odd years that I’m aware of.
Once with my diabetic nurse I was an hour late (due to people in london not realizing you ride in the tube not under it) & they still managed to squeeze me in at the end.
The second was the annual eye test, they’d given a weeks notice for the appointment, during three weeks I wasn’t in the country. (I received the appointment letter & a snotty letter about missing it when I came back & sent an equally snotty letter back!)