I know, and you don't have to. (Actually, you don't even need the copyright notice at all -- copyrights are valid without it -- but it's a good idea anyway.)
In fact, you shouldn't update it. If you write something in 2002, someone steals the code in 2005, and in 2007 you change the copyright to read "copyright 2007", then later it becomes an issue, the person who stole it can claim "Look, my version is earlier!" and you'll have to go through the explanation of what happened and perhaps provide proof of it, which is an argument you wouldn't have had to make if you'd just left the copyright notice alone.
In fact, you shouldn't update it. If you write something in 2002, someone steals the code in 2005, and in 2007 you change the copyright to read "copyright 2007", then later it becomes an issue, the person who stole it can claim "Look, my version is earlier!" and you'll have to go through the explanation of what happened and perhaps provide proof of it, which is an argument you wouldn't have had to make if you'd just left the copyright notice alone.