I think part of the problem when examining these rifles after many years of commercial (private) ownership is we have no idea the misuse the parts have seen. A bolt head could have been swapped for tighter headspace but not properly fitted. I've actually seen guys take an OA torch to a cocking piece to "slightly soften it" so they could cut it with a file while "match tuning" their "deer gun". Things like this make failures both more likely and more difficult to attribute.