The Carb Value on the receipes don't match up with other values I have e.g. the recipe for Cream of Mushroom Soup gives value of 454g of mushrooms as 1.82g but when I got a listing of carbohydrate values from another web sit it says there are 5.29g in 100g - I am concerned that I am now eating more than the 20g a day recommende
The recipes show all carb values as net carbs. The 20g a day limit you mention is net carbs. Many countries including the UK show the fiber and 'net' carb content of a product separately on the nutrition label. However, in the US, nutrition labels include the fiber count within the total carb count. But to do Atkins or other low carb diets, you don't need to count the carbs from fiber because the body can't digest them. In fact, 20 g of carbs a day wouldn't give you much to eat at all if you ate a lot of healthy low carb food like salads and non-starchy veggies and you were counting the fiber carbs!
When you're looking up carb counts in books or online databases, you have to be careful to check whether the counts are shown as carbs-including-fiber or net carbs.
Getting back to the Low Carb / Low GI Cookbook, it is designed to cope with whichever way you want to deal with the carb values. As already mentioned, the carb values are net carbs, but if you prefer to count carbs-including-fiber, you can adjust the carb counts of each ingredient in the recipes and it will automatically retotal them for the recipe for you.