For years before 1900 and after 1999 the return is browsers dependent.
Internet Explorer – returns four digits for years before 1900 and after 1999.
Mozilla/Firefox – it returns a value of 100 or greater for years >= 2000. In my case, instead of the year 2009, 109 was returned.
There is a separate function to get the correct year called getFullYear(). Use that and you should be just fine.