Dates shifted about copying sheet to new workbook

Hi all,

I've a mystery I had try to solve for some time and can't figure out where to start. I inherited a very simple single-sheet Excel file with names and dates in it. When I make a copy of this sheet to a new workbook, all dates are shifted by roughly 4 years (e.g. 1/28/2014 becomes 1/27/2010). I tried to insert a couple blank sheets and move the data sheet (instead of copying it) to a new workbook to no avail. I have examined the date field and found the issue in the source file. When I change the format of the cell with 1/28/2014 in it to "general", I get 40205 (incorrect) instead of 41667 (correct). And when I change the cell format back to date, I get 1/28/2014 once again. If I change the cell value to 41667, I get 1/29/2018. Anyone has any idea what I can do to fix this problem?

Thanks.