When you paste a row of dates into an excel spreadsheet, the dates change all wonky. Here’s why…
So, it turns out you’re not insane. You’re simply trying to copy from (and paste to), different versions of Excel, one being a PC-based version and the other MAC.
Why can’t MAC and PC just get along??? Sigh.
By default, Excel for PCs uses a 1900 date system, whereas MAC Excel uses a 1904 date system. This causes some interesting copy/paste issues but it’s easy to workaround. You can either change the default action of Excel, or just adjust the dates as you go by adding 1462 to your dates. Choose the option which best fits your application.
Here is my selected resource on this subject which will tell you how to apply the 1462 fix as well as more than you ever wanted to know about the date systems: http://www.tuaw.com/2009/07/30/what-to-do-when-the-wrong-date-is-pasted-in-excel/