Other factors could be alcohol which is 7 calories per gram, and may not be listed, and Insoluble fiber which doesn't get absorbed into your body, so may be counted as a carb, but not in calories, or vice versa.
Labeling is pretty bad, but it is uniform. Just find a set point at which you lose, and stick to it. weight loss X time = success. If you are losing, don't change a thing.