You have covered the subject of spring failures through unfinished
ends many times. Most of my working life was spent in the spring-making industry producing large hot-rolled springs with diameters that allowed people to stand inside, as well as standard springs for cars, lorries, shavers etc. The suspension and valve springs for the auto trade were very carefully end ground on both ends and the consequent stress relieving very tightly controlled. When designing highly stressed springs we always pointed out the desirability of the ends being ground or squared off; but, as usual, there were those who knew better resulting in many cases serious failures.