UtilsFIRST_VALID_EXCEL_DATE Field

All dates before this date are shifted in Excel by -1.0, since Excel assumes wrongly that the year 1900 is a leap year.
See also: https://docs.microsoft.com/en-us/office/troubleshoot/excel/wrongly-assumes-1900-is-leap-year

public static readonly DateTime FIRST_VALID_EXCEL_DATE