Nutrition_facts_discrepancies_which_one_is_correct/

So I’m wondering about the calories in this loaf of bread... if you calculate by grams it’s 1500-1600kcal if by slices it’s at least 2000kcal The total weight is listed at 681g and facts say that 120kcal per 54g slice but it also says that there are about 17 slices, (works out to 12. Something if going by grams that’s quite a bit of rounding up... so which is right? Being one of those (often eat a whole 1/2 kilo in one go) freaks this makes a huge difference... Oh and this isn’t a Pullman loaf so the slices are all different sizes anyways basically I’m asking if the error is more likely to be in the serving size or the number of servings per unit. (do I go by the kcal as calculated by serving or by grams (there are less servings if divide the total weight by grams per serving than if multiply the number of serving per loaf as stated on the package like you would usually do to get total calories..my question is which number should I be attributing to those grams that I’ve eaten since the nutrition facts is inconsistent)