Sometimes W|A gives you something ...
WolframAlpha["electricity production of the United States in 2007", "Result"]
... not available in the WDF
CountryData["UnitedStates", {"ElectricityProduction", 2007}]
Other times, the opposite seems to apply - say for more recent data in WDF ...
CountryData["UnitedStates", "ElectricityProduction"]
... whereas in W|A
WolframAlpha["electricity production of the United States in 2014", "Result"]
... or at least I'd assumed it was more recent and this now conflicts with the earlier W|A output?
CountryData["UnitedStates", "ElectricityProduction", "Date"]
Are multiple data sources being used here or is this a bug?