Remember how Lotus 1-2-3 considered 1900 a leap year and how that was faithfully copied to Excel? Because it adds an extra day to 1900, many date calculation functions relying on this can easily be off by a day. That means that 39082 might be January 1st, 2011 (on Macs), or it might be December 31st, 2006 (on Windows). If my “year parser” extracts 2011 from the formatted value, well, that’s great. But since the Excel parser doesn’t know whether it’s a 1900 or 1904 date system, it defaults to the common 1900 date system, returns 2006 as the year, my software sees that the years are five years apart assumes an error, logs it, and returns the unformatted value.
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