In theory, and in practice for that matter, alchemical products were poor ingredients.
While Liam's training and every alchemical master strived for perfection, no such thing existed. There were levels of greatness, but no apex.
Moreover, variables always appeared. They weren't the product of the alchemist's inexperience. They just happened naturally, demanding fixes that left traces in the alchemical product.
Of course, those traces were less than negligible in completed, successful alchemical products. They wouldn't actually affect anything in terms of the pill, elixir, or whatever's effects.
Yet, those traces of imperfection would return if someone used completed products as ingredients. Actually, they would appear in far grander fashion than natural variables since they were the result of a series of improvised fixes.
