XlsIo DateTime Incorrect by about 4 years

Question

I'm using the XlsIo .net library and it seems to consistently return a date that is four years and one day in the past compared to the value I see in Excel.

Does anyone know what the cause of this is?

Answer 1

Excel has an option to use use the 1904 date system. This is turned off by default. I wonder if it is either on, or if the .net library is using that for it's calculation.