In the US, food manufacturers are required to list the calories for the food product as it is packaged, without any other preparation. They can optionally include the nutritional data for the product as prepared, but must clearly label it as such (and still have to include the nutritional data for the product as packaged, so there would be two sets of nutritional data).
So unless there are two sets of nutritional data on the box, what is listed is for the cake mix as packaged.
You can find out more than you ever wanted to know about US requirements for nutritional data at
http://www.cfsan.fda.gov/label.html.