From what I can tell, when you get 100%, building things from your kit (Undead Bait, Boom Bait, Phosphorus Coating, Blunderbuss Ammo) no longer use up or require ingredients such as flowers/herbs or even Dynamite in the case of Boom Bait.
So in a sense you can have unlimited phosphorus rounds, even if you don't have Violet Snowdrops. It would only last for a short while but you can keep selecting it from your kit. . --- Rereading your texts hurts better than cutting.