When you renamed the catalog, did you also rename the folder it is in? I am thinking that LR expects the .LRCAT file to be in a folder with the same name. If the folder name and .LRCAT name differs, LR finds or builds a folder of the .LRCAT name and places the backup file there.
I've really no idea how LR works, but, as a retired application and system programmer, I can see this happening.
Best of luck finding your backups,
Alan