Software Deployment

I have a package that I'm working on and there are 3 previous versions that are installed in my company. I have the previous MSIs and added all of them to the upgrade table so now i have 9 upgrade codes in the table since all of them use different upgrade codes. During my testing i install a previous package and then install my new package but the new package doesn't uninstall the older version. Does anyone have any ideas why this isn't working?