Even the Lore of Vampires can't be that easy. It took a towering genius building on five hundred years of magical research into the metaphysics of death and the soul combined with the millenia old dark elven dark magic secrets to invent any kind of necromancy, which was a revolutionary advance on the arts of the Mortuary Cult, whether it used Shyish tongs or not. They couldn't work out how to animate bodies, only bind souls to them (living or dead).
Creating spells to raise undead seems to be a genuinely very hard thing to do, requiring detailed knowledge and understanding of how to bind which type of fragments of a soul to their former body to animate them in various forms. Manfred Von Carstein is quite explicit, and he should know. He says 'Great difficulty surrounds the study of necromancy. To learn the art, an aspirant must either find a necromancer and become his apprentice, or acquire one of the forbidden books of necromancy such as the Liber Mortis or one of the Nine Books of Nagash.'. Note the 'must'. Making it up as you go along isn't presented as an option. He even discusses what kinds of things are needed from those books, such as the secrets of dead spirits and how to summon and bind them.
As a note, we can't forget the third key part of Necromancy as described by Manfred. It isn't just Shyish + Dhar. It's Shyish + a dead body or soul (fragment) + Dhar. That middle part seems essential. The Shyish appears to be used to manipulate the dead thing as a channel through which to control the Dhar. It seems similar to how Thaumaturgical ALchemy is described, which is Chamon + a chemical reaction/material object + a second Wind. I wonder if the reason that the Gold College keep it such a secret is that it looks a lot like Necromancy in principle.