We managed to all our multi-backups with PS Elements and finally saved unique copies of all photos in one place: locally on our computer. A folder with 100,000 files (260 GB) was generated by PS Elements.
Now, after a while, we tried to make favour of the PS data collection. But if we try to open a thumbnail image, we get an error message from PS. PS tries to find an image with it' s original name in the data collection folder. But in this folder, images are alle renamed (by PS elements, we guess).
Obviously, the data are present, but PS Elements has forgot how to access them.
It is not entirely clear what you have done or what you are trying to do.
It appears that the catalog you are using "to make favour of the PS data collection" is treating the catalog files as missing. This happens when you have not used Elements to move the file from one location to another on your drive(s). First you have to be clear that when you create different catalogs and import the same photo into each catalog, Elements does not make a copy of the photo. The photo remains wherever you first stored it on your computer.
If you have restored multiple backups from several different catalogs, you may have been able to move and store unique copies of your photos in a single folder e.g. a My Pictures folder, rather than multiple copies of the same photo in different locations. Is this what you did? You can only use one catalog at a time, and you cannot combine catalogs internally. So, if you made a backup of two different catalogs each of which may have had the same photo within them, when you restored one of the catalogs and changed the location of the file (to a common folder), the other catalog has no idea of what you did, and if the same photo is contained within the second catalog, the moved file will show up as missing.
I'm just guessing what you have done, but hopefully I have given you some idea of what the problem may involve. If you give us more details, we may be able to help you out.