Sigh. I found so many ContentManager.xml files in the various subdirectories of AppData\Roaming\Steinberg, edited all of them to point to the new location, and this didn’t help cubase locate the .vstsound files.
So I went ahead and manually located every library on my next Cubase startup. Some configuration file is still pointing to the original location on my C: drive, and so Cubase ended up creating shortcuts to all of the “missing” VST libraries.
So, long answer short, you’ll definitely want to create those shortcuts and put them in the original location, even if you use Library Manager to move the contents to another location.