Limbsplit upgrade

I have been trying to upgrade my Limbsplit, but have been unable to despite killing Hammerstorm with the weapon equipped and in inventory. After five kills without any luck, I'm wondering if there are some other requirements outside of those listed on https://pathofexile.fandom.com/wiki/Severed_Limbs

That PoE wiki is out of date and is not the best one to use in any case.

Try https://www.poewiki.net/

Prophecies have been removed, so there is no way to use them to upgrade items any more.