Versions of Microsoft Word before Word 2007 had the following annoying bug:
Consider an Excel spreadsheet with the following data.
|Name||Date of Birth|
The astute will notice the dates are in Day.Month.Year format.
Now we mail merge into Microsoft Word
Ed Apple 12/3/1978
Fred Pear 04/12/1956
Rosemary Peach 12/04/1968
Notice that the date is now in Month.Day.Year format.
Microsoft KB article 325579 has further details.
The workaround is to manually edit the MergeField to explicitly format Day.Month.Year.
The fix? Word 2007 resolves the problem.