One somewhat befuddling issue you may come across is that in the USA thy use a different method of counting the carbohydrate content to that we use in the UK. Here we count fibre content
separately from carbohydrates, in the USA it's
included and has to be subtracted to calculate
net carbs, and this net carbs figure is then equivalent to our (total) carbs.
Unless you're reading the actual packaging nutritional content, you may need to be aware of which country any information is applicable to.
Also be aware that for fruit and vegetables, different growing conditions and varieties may result in differing amounts of carbs so that you are always likely to get some (small) differences in values given.
Any site that relies on user input may well contain inaccuracies as it's possible that data has come from unreliable sources. The best you can ever hope for are fairly approximate figures, so don't get too fussed over very precise ones.
Robbity