Talk:Souls of Lords/@comment-75.161.17.222-20150112074105/@comment-4511886-20150112121833

Because, it's a big enough piece of that soul to satiate the lord vessel. I guess technically speaking, the Lord Soul Shard of the Four Kings may have been corrupted by humanity, along with the kings, which would make it count as the Dark Soul.

By the way, Sif doesn't drop a lord soul. Just the means to get one of them.