[Karellen]

when I did a test run with just one new classification, Comedy Movies and added the folder as a separate source, the files scanned perfectly and the titles show up in File Manager, but they've not been added in the main Movies library

Just check you followed the correct procedure to add a new Source... https://kodi.wiki/view/Adding_video_sources

If items have been scraped correctly, then they will end up in either Movies or TV shows, depending what you nominated for the Source.

You can also use Smart Playlists to separate your media. If you are using Estuary, you can't create new menu items, but you can add the Smart Playlists to the Favourites menu and access them from there... https://kodi.wiki/view/Smart_playlists

[Bert Coules]

Just check you followed the correct procedure to add a new Source... https://kodi.wiki/view/Adding_video_sources

I certainly thought I had but I'll check, thanks. 

You can also use Smart Playlists to separate your media. If you are using Estuary, you can't create new menu items, but you can add the Smart Playlists to the Favourites menu and access them from there... https://kodi.wiki/view/Smart_playlists

Smart Playlists is something I haven't looked at all yet.  I'll give it a try.

[Bert Coules]

Karellen,

Another update: I did set up the new source correctly but  I didn't twig that I then had to refresh the library.  With that done, the titles appeared.

As well as Smart Playlists I'm wondering if I could somehow group the related titles together as a Collection; I'll look into that.

[Karellen]

With that done, the titles appeared.

Great!!

As well as Smart Playlists I'm wondering if I could somehow group the related titles together as a Collection

By Collections, you mean Movie Sets? Probably not a great use for Movie Sets as a movie can only be used in one Movie Set, which means you will break any actual Movie Sets that may exist for those movies.

With Grouping, Smart Playlists is the best way to go. If you change to a different skin you can add that Smart Playlist to the main menu.

There is also Universes, but probably not for what you are trying to do... https://kodi.wiki/view/HOW-TO:Movie_universe

[Bert Coules]

By Collections, you mean Movie Sets? Probably not a great use for Movie Sets as a movie can only be used in one Movie Set, which means you will break any actual Movie Sets that may exist for those movies.

That's interesting.  I used that term because in a previous update of the Movies library Kodi automatically grouped two titles into what was labelled a Collection.  Rather neat, I thought, if it can be controlled.  Perhaps this is Movie Sets under a different name?

Thanks for the tip though: I'll look at Smart Playlists.  While I'm still getting used to Kodi I don't want to move away from Estuary (which I rather like, anyway) but the idea of being able to customise the main menu in some other skins is attractive.  Oh, and:
 

Great!

Yes!  Very satisfying that I worked that last bit out for myself.