As long as the OD of the retainer covers half the wire diameter of the spring, you are good. If spring tips are breaking off, it is not the correct spring for the combination, tips that turn blue are telling you the exact same thing.
the thing is i've been using these type of springs for a decade but only noticed problems when we changed to the tool steel retainers, & the problem only surfaces on the second season of use, at first we thought they had gone soft but thats not the problem, they test up ok & we're not seeing any signs of valve float.