In the US, the FDA has not stated how a company should determine the nutrient content of their product for labeling purposes. Therefore, there is no prohibition from using "average" values for a product derived from databases if a manufacturer is confident that the values obtained meet FDA's compliance criteria. Regardless of its source, a company is responsible for the accuracy and the compliance of the information presented on the label.
Source: Food Labeling Questions and Answers, U. S. Food and Drug Administration, Center for Food Safety and Applied Nutrition Booklet August 1993.
Similarly, Health Canada states, “The industry is responsible for complying with all the requirements for nutrient composition and the accuracy of the information provided on labels. The means of developing label values and choice of nutrient data source is the responsibility of the party selling the food and that provides nutrition labelling. Companies or organizations developing nutrient data for labelling purposes should employ appropriate procedures for analysis and sampling as well as statistical treatment of data to ensure that product labelling would be in compliance. Where using nutrition labelling databases or nutrient composition tables, they should ensure that the data are of adequate quality to provide a basis for nutrition labelling; they should have procedures in place to ensure that label values accurately represent the nutrient content of the food within the above compliance parameters."
Source: www.inspection.gc.ca Canadian Labelling, Use of Nutrition Labelling Databases or Nutrient Composition Tables