Symantec reverting to older version

I've never had this happend to me personally, but there is another employee who I work with that said when he installed the new version of symantec (12.1Ru4) he came back to that machine and it had reverted to the older version that was previously on it (12.1.1). Is this something that can happen? I thought to even go back to an older version you had to uninstall and reinstall it. Any help would be appreciated. Operating systems xp and win 7.

Thanks,

Stephanie