You can track deleted appointments which means they will still display on the schedule.

Click on File, System Options, Global tab and check the box below.

Deleted reservations show as gray lines with black text on the schedules.

There is also a tab on the pet card that will track deleted appointments.

Open the pet card, click on Notes, Appt Notes tab.

There is a section that will track No Shows, cancelled and deleted appointments.

This is so you can turn off Track deleted reservations but still see them listed on the pet card.