This is a manual operation, adding photos to folders does not change the collection membership. You'd have to add the photos to the folders, import them, and then add them to the desired collection.
A simpler process is to use default folder names such as capture date (which eliminates a step from your process), import the photos, and then add the photos to the collections.
If you're changing the *photos* in the folder, they will show up in the collection with no action necessary. If you're adding or deleting photos in the folder, unfortunately there isn't a good way to update your collection.
Smart collections could give you the dynamic result you want, but so far, we are not able to sync smart collections to LR mobile. You'll just have to select all the images in the folder and drag to your collection (Duplicates will be ignored and only new photos added).
If you're changing the *photos* in the folder,
Does "changing" mean "editing", or something else?
Thanks for that Mike. I have deleted some files and added new ones, in my folder. I have just tried, as you suggested, dragging and dropping the whole folder to the collection expecting it to 'move' the new files to the collection but still leave the deleted ones.I could then manually delete the files I no longer want in the collection.
But surprise surprise, after the d & d, both the folder and the collection are identical.
I've just checked my smartphone and that's identical too.
Many thanks, Tony
Thanks for your help,but have a look at my reply to mhoffman.
When you delete a photo from a folder, you are deleting it from Lightroom's catalog. So, any collection containing that photo will automatically have the photo removed.
Keep in mind that collections in LR are kind of like play lists in music software like iTunes. You can add and delete any songs in your music library to one or more playlists, but you only have one copy of the song. If you go to your library and delete the song, it is gone from all the playlists as well.