Can anyone tell me why nutrition labels on most everything differ from the real carb count (or what fitday reports)?

The major cause of differences that I have found is the serving size given by each. When you use fitday, be sure that you set the serving size to what you want.

It's not always that. Sometimes it has to do with preparation method.

But somehow, labels often have 'hidden carbs'. You can check that by going to the calories.

Compare the calories per serving as stated on the label.

A - Then go to the Protein and multiply the number of grams x 4 calories
B - Add the Fat by multiplying the number of grams x 9 calories.
C - Add the Carb by multiplying the number of grams x 4 calories

The total of A + B + C should equal the stated calories. If not, there just might be more carb calories than stated. If it's only off by less than 5, it's probably due to rounding up or down.

Those are some of the reasons. I trust the USDA food charts and Corinne Netzer's carb counting books.