Corpses in harvest

Hi guys, I'm playing my first Necromancer and I'm trying to find specific corpses in Harvest, but I can't get the corpses after killing them. I tried without using Bone Offering, but it's the same.

After killing them, I used Desecrate, but I still only get my old Host Chieftain corpses and not the ones I want. Am I doing something wrong, or are the corpses just really rare?