[possible spoilers]
There are 18 unique stews. There are 56 recipes. You do the math.
Just as there is often more than one road leading to the same city, there is often more than one recipe leading to the same stew.
Your confusion lies in your belief that you should get credit for each unique recipe. However, credit is not based on unique recipes. Credit is based on finding unique stews.
Let me illustrate with a fictitious example. If you find 15 different recipes to make a stew that causes fire to shoot out from your bottom, you might think you are deserving of 15 credits. You might think that.
But that is not what will happen. You have only discovered one of the 18 unique stews - the "Montezuma's Revenge" stew. One. Not 15. So you get one credit. One credit for the "Montezuma's Revenge" stew. Not 15 credits for 15 recipes. You get only one credit for the one stew, and you also get a very sore bottom.
Although most of the 18 unique stews have multiple recipes, not all do. There are a few that have only one recipe.
For a complete list of stews and recipes click on Stew Recipes in my signature.