in order for ingredient effects to show up in the book, you have to drink a potion containing that ingredient, I believe the 2nd npc tells you this
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Just went back and checked. The poor woman asks for some poison to get rid of her competitor, but she doesn't mention anything about being able to drink potions. The controls at the beginning don't mention it either. Just looked again and it's there, I must have missed it. Even if it does mention drinking potions, it doesn't tell you that drinking them will reveal their effects. After testing, I see that you have to press space while holding a filled potion to drink it. I feel like it would be best if the ingredients reveal themselves to the player after using them in a potion, rather than drinking them. Since the NPCs don't tell you what drinking a potion does (I went through several days of NPCs just to make sure, none of them mention it) it makes that mechanic look like a bug.
Don't get discouraged by that though, if you end up fixing this after the voting period is over that'd be cool.