Consider this:
Someone drops their belay device, and asks the question, "Do I need to buy a new one?" Typical response is, "Isn't your LIFE worth $25?"
So most people consider the cost/benefit ratio and "buy the argument" and go buy a new one and retire the old one. So it never gets used again. Ever. So we never learn if it would have failed or not.
Now, occasionally, someone will NOT replace the dropped device. Did it eventually fail? Or did he/she just get lucky all these years? We'll never know that either.
I know it doesn't exactly answer your question, but I'd posit that that's the way it goes the majority of the time. YMMV.