You can exploit the fact that when copies of the originals are made, they are not selected. Thus, when AppointmentsDragComplete fires, if appointments were created during the drag operation, the selected appointments are your "logical" copies:

private bool isDragging = false;
private bool hasCopies = false;

void calendarInfo_BeforeAppointmentAdded(object sender, CancelableAppointmentEventArgs e)
{
    if ( this.isDragging )
        this.hasCopies = true;
}

void dayView_BeforeAppointmentsMoved(object sender, CancelableAppointmentsEventArgs e)
{          
    this.isDragging = true;
}

void dayView_AppointmentsDragComplete(object sender, AppointmentsDragCompleteEventArgs e)
{
    if ( this.hasCopies )
    {
        //  The members of the SelectedAppointments collection are copies
        //  because the original appointments were not selected when they were created.
    }

    this.isDragging = false;
    this.hasCopies = false;
}