Registry backed up automatically? Then why my problem?

A few months ago, I had a problem on startup of my Win 98 SE machine.
Windows told me it had found a problem in the registry, and that it
would use an earlier registry backup. Well, that backup turned out to
be several years old!

I ended up having to reinstall everything. So today I got the idea that
I'd better make a backup of my registry regularly.

So I googled for instructions on how to do this and found many sites
with the following advice:

"click Start and select Run. In the Run dialog box, type scanregw.exe
and click OK. This will check the Registry for errors. When the scan is
complete, a dialog box will display the following message: "No Errors
Found. The System Registry Has Been Backed Up Already Today. Would You
Like To Back It Up Again?" Click Yes to perform the backup. When the
backup is complete, a new dialog box will open, saying Backup Complete.
Click OK."

Well, this suggests that the registry is being automatically backed up
every day. But if that's true, why did Windows restore a registry from
several years ago when I had my problem? And how can I be prepared if
it happens again?

Thanks for any answers.