Reason I asked the question about lock wiring of prop bolts was a friend of mine used to work with the Australian ATSB (equivalent to USA NTSB). He was investigating an accident where the aircraft lost a prop and the resulting landing involved a serious injury. Turned out the prop bolts were not positively locked in any way. They merely relied on torquing of the bolts, not even lock washers, and it was a wooden prop. Whether it had a crush plate I can't recall, but for me, it's a no brainer - some form of positive bolt retention is critical.