Dave Wilkins says None of our software will copy the same file again if it already exists (and matches) on both sides. We only resolve 'differences'.
However, I have just run SyncBack V6.5.30.0 and it prompted me that two files were only on the right and offered to delete them etc. etc. from the left. BUT the exact same files are definitely still on the left and in the same root folder and sub-folder! I find this quite worrying, as I usually just instruct it to delete the file(s)from the left.