BleepingComputer.com: Upgrade apps on backup drive?

This is probably considered a dumb question, but I sincerely don't know the answer..

For a bit more than a year I've been doing weekly backups to an always attached Seagate external drive. When I run an application like Secunia to check for out-of-date or insecure apps, it reports on those on my C drive, as well as those on the external hard disk. Should I be updating the applications on the backup drive too? I'm thinking that since it always attached, it could easily be a source of problems, but on the other hand, don't I need the older version of the app to use my old data if I need it? Luckily I've never needed anything but a couple of Word docs from the backup drive. Or, can/should I delete the applications on the external drive and just leave the data behind? I tried to use the Install/Uninstall Utility to get rid of one, but it only looked at the C drive.

Any advice? (I did try searches and looked for tutorials prior to posting, since I can't be the only dummy who wants this information, can I?)

Thanks for your help.