If you are curious to know how Excel stores dates and times, please check out part 1 of this tutorial - Excel date format.
You can type a date in an Excel cell in a variety of ways, for example 1/1/2015, or 1-Jan-2015, or 1-Jan, or January 1, 2015.
I have a specific letter template that I like to use when I'm creating business correspondence.
I always remember to type in the recipient's name, address, and of course the body of the letter. I print out the letter and - if I'm lucky - I discover that it has an old date on it.
See how to insert today's date and current time as static time stamp or dynamic values, how to auto populate a column or row with weekdays, and how to auto fill random dates in Excel.
There are several ways to add dates in Excel depending on what exactly you want to do.
So, what I do is just make sure to save the file as "letter to joe smith 2004-11-01.doc" for example.