I did a search on my archive disk, without luck, just the '97 version.
The only hit for the earlier was an old winmag article about it.
. . .
Btw, if perchance you want to view the undo.reg file generated by MS
Regclean, one way to go is using a .reg file viewer.
http://www.utils32.com/regview.asp.
It loads for view a .reg file from disk, disconnected from the registry.
It gives the same hierarchical layout as a registry editor. I admit that
it's only that company's pay product which gets more interesting, in its
letting you interact from that file directly with your registry. But the
freeware viewer can be handy on occasion. At least it does let you copy
a key path to clipboard, so you can then go view any keys in question in
your actual registry, with your reg editor.