Since the Nutrition Facts label lists only the items that are required by law to be listed on food products, Potassium, Ca, Mg and folate may be listed as percent daily values, but not exact amounts. They also aren't listed in the data base. This will make your reports inaccurate unless you are entering the nutrient amounts yourself using a more comprehensive tool.
If it is important to have accuracy with micronutrients because of a medical condition, you can enter each food item yourself (and save in your favorites for easy access moving forward) to include all nutrition information. The food list from the USDA can help. ndb.nal.usda.gov/ndb/search/list