Tee Emm, I think those accidents illustrate failure to prioritise rather than mechanical failure leading to inability to feather. All except for the Camden accident, which was instructor stupidity.
Whilst you have answered slippery_pete's question, I think he was actually referring to Centaurus' scenario of catastrophic bearing failure leading to a seized propeller. Like you, I'm not aware of any scenarios like that in recent years.
I did once suffer a mechanical malfunction in a light twin, causing cycling of propeller RPM without any change in engine power. I feathered the propeller at the high point of RPM without going through the full drill, for the reasons Centaurus explained. But that was in the cruise, at low workload. I devoted my full & undivided attention to which propeller was malfunctioning and which propeller control I was touching...