reading this I keep thinking the real questions are: 1. probably the notice sending and db deletion is two separate teams or responsibilities. Are they? 2. Did people know there was a bug in notice sending so some notices were not being sent, all notices not being sent? I ask this because generally in places I've worked where notice sending was an important part of things you knew if there was a bug and notices were…
Note that this is not to say the end result wasn't an indefensible disaster, only that disasters seldom have only a single cause and the above is my best uneducated guess at how things came together to cause this one.