How do you account for, or guess is, the cause of breakage?
1) Old tech material failure like early "rubber" compounds. Things dry out, embrittle and arc.
2) Flawed material e.g. imperfect wire or connection point? Weak point burn out, failure to conduct electricity etc.
3) Control electronics? Sure, it's gotten better since the '50's (dawn of Fuel Injection) but still fail occasionally.
Since consumer products have "infant mortality" or last a long, long time, what constitutes "infant mortality" in the production and QC of coils?
As reported here: I contacted a big Volvo parts source regarding the separate coils (COP's, not a pack or cassette) used in Volvo 5 cylinder engines ca. 1983-2009.
The seller said he stocked them and has never sold one.