Every couple years the company updates to a newer version of MS OFFICE and I have to make changes to my spreadsheets because the new version does something weird to my spreadsheet.
Every time they announce that a MS update is going to be pushed I get nervous.
Other people use my spreadsheets on backshifts so I figure I might be getting a call in the middle of the night.
Try using a date prior to 1900 in an Excel spreadsheet.