>>96939948
>>96939953
It's how the gods have worked since the start, to make one and its roster of demons you need a type of greater demon, a type of lesser demon, a type of beast and a type of steed.

And nurgle as a steed used a palanquin carried by nurglings, a solution to the discrepancy would be claiming that all of the various mounts nurgle uses are deep down puppeteered by nurgling parasites, I guess.