Good to know, @Steve C. I have had good luck with PatchCleaner myself, but I've always archived the cleaned-up files on another drive "just in case." Never actually had to use them, but it helps to hear that some clean-ups don't achieve trouble-free results. May have to re-think my recommendations for and personal use of the tool.
Thanks again,
--Ed--

PS: Right now, amusingly enough, PatchCleaner on my production desktop emits this status window, which could be described as "Move along folks. Nothing to see here."
Can I Safely Delete These Files in the Windows Installer Cache?-image.png