database different values

Just want to say i've noticed that database food items have different calorie value than whats on the box. kraft brand Mac & cheese is 1700 calories prepared according to database, but only 250 per serving or 500 for 1 box prepared. 1700 is a lot more than 500. 500 is without milk and butter, but its only 280 calories for 1/2 box prepared with milk and butter as per directions.
If you're not losing weight and don't know why make sure you get the right calorie value. I scanned my kraft brand mac and cheese UPC barcode and it came up 290 calories. No where on the nutritional label does anything say 290! I have no idea why the upc says 290. it is 280 prepared according to the box (and 250 without milk or butter, as I make it).
So be dubious about your numbers make sure you are getting the right values. There are many ways you can get tripped up!

editited for typos