Whenever you result an appointment as not sold, you get the option to "Create an Appoinment" as the next step. When you do this, the system utilizes a field called "Previous Appointment". The appointment which is created after selecting this option will copy the name of the old appointment into this field.
Why is this useful?
After the fact this is useful for you to report on reset appointments against their original appointments. It is a seldom used feature because it does limit your options to JUST the original and resulting reset appointment. Perhaps the easiest way to incorporate this in a report is to use that "Previous Appointment" field, this would allow you to see any appointments(appts) with previous appts.
Alternatively, you could use the report type of "Appointments with Subsequent Appointments". This would show the first, unsold appointment and then the related subsequent one.