Are the brands the same?
If not, then it may be as simple as different labs testing the dates submitted as test samples by their respective companies.
If the two are of the same brand, then it may be a matter of what dates were submitted for test results and when. A company is not required to test the produce the use from year to year as to nutritional value. The results from a test in year "X" may be used for several years since the tests are NOT cheap to have performed.
Sugar content of a specific type of fruit can vary from year to year based on rainfall/watering rates during fruit maturation. Some varieties produce sweeter fruit when they have had the exact right amount of water at just the right intervals. Orchards relying on a combination of rainfall augmented by irrigation have ups and downs in watering rates, which also affects fruit quality. A grossly over watered tree will have diluted sugar concentrations as the resulting larger fruit still have the same amount of sugars as the smaller fruits. (This is also variable based on the fruit in particular as well as WHICH variety of fruit trees are being harvested.
Batch "X" of dates may be sent in for testing with the intended use being "Whole, pitted" and batch "Y" sent in for "Diced". The sugar content of the independent batches could be different based on the factors above, or any number of other factors I failed to mention.
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