MacBook Pro keeps 'updating'

My wife's 13" MacBook Pro (Late 2011) is running Snow Leopard, and every time I run Software Update, it shows the same 15 or 20 updates that are needed- even though I have run Software Update several times in the past and *supposedly* downloaded and installed those same updates. There are a couple firmware updates included in this list, which I assume should have also updated. Every time I've run the update process, it shows download and install progress- even to the point of restarting the machine- but the same available updates show up when I run Software Update again. How do I know that these updates are actually installed- and if not, how can I get them to actually complete the installation? I know checking the version numbers of specific apps, like iPhoto, would indicate that actual updating has occurred, but that doesn't explain the firmware updates constantly being listed.