You can't add FTDs together and expect to reach any meaningful value.
It is like taking roll call in a classroom and adding all the absences together for the year then saying that there were 300 children missing from a 30 child classroom.
The ftd list is cumulative. That means that every share that has not settled to the present day is on the list. You can't add yesterdays list to todays because if yesterdays shares have not settled then they are included on todays list already. The current list is EVERY SHARE that has not yet settled, every one.