I dont think I've even heard of 9 BHN clip on WW.
That was a left-over ingot of WW cast about 10 years ago -- i.e., "aged" -- as was noted. Aging does
soften antimony-lead alloys considerably over extended time, so that 8.9 was real.
Believe me when I observe that with rare exception, alloys whose BHN numbers make-the-rounds on the internet are generally far softer than the "accepted" internet sources say they are. Numbers get repeated without actual test. If you want truth and no-kidding experience, swing over to castboolits.gunloads.com and open up the "Alloys" section.
I will offer in closing that the truly "Hard-Cast" bullets by the professional caster are
hard -- witness the ~24BHN of Beartooth's 400gr LFNGC at the bottom of the chart above.