Excel for Windows uses a date formula starting from January 1st, 1900; however Excel for Mac 2008, and any earlier versions, uses a date formula starting from January 1st, 1904. Excel for Mac 2011, and beyond, have switched to the January 1st, 1900 date formula to match the Windows version. 

Steps to edit the setting:

1. Open the affected Excel document.
2. Select File > Options.
3. Click Advanced.
4. Scroll to the setting titled When Calculating This Workbook.
5. Unmark the option titled Use 1904 Date System.

*** Note: Adjusting this setting affects all dates in the current workbook. This setting while not affect other workbooks, only the one currently being worked, so it will need to be adjusted for each export.