Many thanks, folks, for the speedy replies which helped me to work out what was happening.

I had made a mistake when installing: I didn't specify that my content was on a different drive. When I ran the installer again, but configured it to store the content on the D: drive, the missing library items appeared. I'm not sure why it worked like that - I would have expected a huge amount of content to appear on my C; drive when I ran the installer the first time, but they didn't - so perhaps I've got something a little bit odd in my configuration. But no matter - everything working now.

And, of course, five minutes later I found it when I set "Launch to factory scene" in the settings...

However, I still can't find it in the library. Where is it supposed to be?