there is this consideration as well...
A wise necromancer does not wish to fight for control of his creation with an angry spirit seeking a way back into the world. Best to be certain all of a creature's soul has departed before reanimation begins.
https://en.uesp.net/wiki/Lore:On_Necromancy
edit:
though I am a bit confused of the skills needed to reanimate the bones/skeleton of one whose original soul has already left... soul gems maybe?....alchemical recipes of reanimation solutions?