It depends on what you’re using for the extraction. Coconut oil will retain more cannabinoids than butter. I found one source saying up to 80% of that 120mg is retained if you use coconut oil. I believe butter is more like 60%.
So if you’re using coconut oil more like 96mg per cake, if butter more like 72mg.
Haven’t heard that, I apply the loss factor based on the extraction (absorption?) medium. So you only get 80% of potential cannabinoids with oil, less with butter.