Are you absolutely certain the 2012 pictures are in subfolders? Go to 2012 and right click, Show in Finder.
Try selecting a photo and do a Cmd R. Are the pictures in the folders you expected them to be? Sure there aren't any duplicates? Are they in the folders you expected them to be?
Are there any question marks on the thumbnails? What happens when you run Library > Find Missing Folders?
Yes. All the pictures are absolutely in the folders where they are and where the LR catalog says they are. No duplicates whatsoever.
Yes there were some question marks but they have been dealt with by re-locating the folders and pictures. So that each photograph is recognised as being on-line by LR and I can zoom in on each one. No pictures are recognised as being lost or missing.
This is very weird. As I say for the photos in the sub-folders for the main folder 2010 and 2011 all of the sub-folders are in the folder's panel. But for 2012 there are 8 sub-folders. All the photographs in the 8 sub folders are within the catalog, all are accessible (i.e none are said to be off line), but only one sub-folder is listed in the folders panel - and that particular sub-folder has 15 sub-folders of its own and they are all recognised.
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This is really a bit of problem since my daughter files her pictures by folder and not by keyword. So she can't find a lot of her pictures.
I started a new catalog which was restricted to only the photographs within the 2012 folder. All photographs were imported and all of the sub-folders are recognised. One solution might be to import from the new catalog, but she has edited over 600 of the photographs in one of the folders and if she then imports from another catalog all those edits will be lost.
Any thoughts
I downloaded LR 3.6 but the same problem persists. I then