When using
<?php the_time('Y'); ?>
in the template to display the year (for example in copyrights statements in the footer), WordPress takes the year associated with the content on any given page.
So if you posted an article in 2006, your footer will show a copyright for 2006 when reading that article. If you wrote a page in 2007, the year will change to 2007 when viewing that page…
If you want to use php for automatically keeping your copyrights up-to-date, use the following script instead:
<?php echo date(Y); ?>