The 100 replacements were due to the battery shutting down due to being over-discharged. As over-discharging can induce thermal runway, the system is designed to shut the battery down when it reaches a specific level of charge. So in these cases, the battery safety systems were operating as designed.
I wondered how the minimum safe voltage was determined? There might well be statistics involved. eg if the minimum voltage is set to X then the MTBF is Y.
That MTBF calculation might be pretty complicated. It might make assumptions about how frequently the minimum voltage is approached? Perhaps if you approach minimum voltage too frequently the MTBF reduces dramatically?