I’m not clear what your second question (on 24 October) refers to, so I’ll try to clarify the matter. I hope this doesn’t come across as over-simplistic, because you are right: the reference in the recently published BSD recipe book is a little lost from view.
In the BSD diet book, on page 183 at the start of the recipes, it states that the calorie counts are for one portion. So if a recipe feeds four people and it says 250 calories, each of the four servings amounts to 250 calories (the total recipe would be 4 x 250, so 1,000).
In the BSD recipe book by Dr. Claire Bailey and Dr. Sarah Schenker, the reference is hidden on page 9 in the introduction: “All the calorie counts in the recipes here are calculated for a single portion, and, in the spirit of pragmatism, we have rounded them to the nearest ten.” So, in the simple egg muffin recipe on page 42 for six muffins, for example, each muffin is the 130 calories detailed alongside the recipe.
If you are looking at other recipes, than that may be a different matter. You can calculate the calorie content of the dishes you prepare by weighing the ingredients and using a calorie calculator or a website or app like My Fitness Pal or Fat Secret, as you are already doing.
I hope this helps.