Check /Applications/Microsoft Office 2004/Updater Logs/.
I don't remember for sure, but I think some of the earliest updates used a
different installer that placed the logs in the root hard drive directory,
so those might be missing from the folder even if you've applied them. That
hasn't been the case for a while though.
You can check the latest update you've applied to Office by navigating to
Applications/Microsoft Office 2004/Office/, selecting the "Microsoft
Component Plugin", and going to File > Get Info, and checking the versio.