If you design a formulaic spell which uses casting requisites now and then, you don't need those requisites for inventing the spell, but only when you cast it with certain targets.
(Parching winds removes water from a target, PeAq. With Co or An casting requisites it can damage animals or people)
If you make an item to be able to do something similar, when do those casting requisites come into play? (can a wand of parching wind that was made without requisites damage people?)