Curious that the second text states that "...in extreme cases the action body has been known to fracture..." Presumably they meant to say the bolt body.
No, I don't think so - In the past I have read reports of SMLE sidewalls fracturing.
I think the examples of fractured bolts has generally been found to be poorly cast (granulated) steel in the bolt body.
Mine are not the best, but they are not too bad. I can think of lots of Enfields I'd rather have but instead of constantly striving for more, sometimes it's good to be satisfied with what one has...