The shredded carrots are added at the end so they don't overcook and disappear into the soup. Also, the tomatoes are added after the beans are tender because the acid in the tomatoes can prevent the beans from becoming tender during the long, slow cooking.
Have small amounts of various leftover dried beans in your cupboard? Mix them together to make 2 1/4 cups of beans, and use them instead of purchasing a package of bean soup mix. Or use a 16-ounce package of dried beans for the bean soup mix, but use only 8 cups of water and 3/4 teaspoon salt.
Add a secret ingredient to this soup for additional flavor and color--stir in 1 cup canned pumpkin when you add the carrots and tomatoes.