Often when I do a full scan, unrecoverable files will appear for days, marked as unrecoverable but still indentifiable from file titles.
Why is this and can I completely remove these files?
File names are not part of the file data but are held in the MFT or Index records, etc. This is where the file name list comes from. Files will be marked as unrecoverable if the file data clusters have been overwritten by other files.
Recuva can't remove file names from the MFT so they will remain on show whatever you do, or whatever the state is, or whether the file data has been long since reused by other files. They may eventuially get overwritten as new files are allocated. They are an irritant but not a great risk.