Nutritional information is "always" a best guess. They are at best, averages. One grape same size and weight, depending on time of harvest etc will contain more or less of various vitamins, minerals, and sugars.
The same goes for all grains etc.
You can place some faith in quality control of what some companies provide but then again, it will be an average.
I find that most data contained in programs like this does vary, but so does the samples.
As long as you can track your "general data" you can get a pretty good best guess for yourself and your nutrition.
Physicians don't even have all the answers to nutrition. I believe what the software is truly about is giving you a "General picture" or "snap shot" over time of what your consuming. It's not meant as a replace for a lab.
People are always welcome to add their own foods from their own nutritional information, but be warned about the ingredients list and putting values in their proper places, like sugar alchohols, fibers, etc.