A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data
The source workbook uses the 1904 date system (standard on Mac) and the other doesn't (standard on Windows).
See https://support.microsoft.com/en-us/help/214330/differences-between-the-1900-and-the-1904-date-system-in-excel for detailed information and instructions on switching between the two systems.