Alt art and/or legacy uniques don't proc their "fated" prophecies.

I have an alt art Kaom's Sign unique ring on Hardcore. This ring is also a legacy version - with life leech instead of the current life gain on hit version.
I got the "King's Path" prophecy that should upgrade Kaom's Sign to Kaom's Way if I kill Kaom while wearing it.
So I did, but the prophecy did not fulfill itself, and my Kaom's Sign did not upgrade.