Often times, after I've run ccleaner's Drive Wiper, I'll run a scan in Recuva to see if there are any files which might not have gotten overwritten. (Sometimes I'll work or surf while it's running, so I know it can't catch newly updated files.) Usually it's only a few files, so I'll just use Recuva's "secure delete". Today there were just some picture files in Chrome's cache (they had viewable "previews"). Their initial state was "very poor". I ran "secure delete" (Gutman) and they changd to "unrecoverable". But I could still see the preview. I repeated the "secure delete" operation, and still the preview was there, but in "unrecoverable" status. Just to see what I would come up with, I decided to recover a few of them. And despite them being listed as unrecoverable, I was able to recover them. All I had to do was add the jpg extension to them and the recovered files looked just as good as the preview in Recuva.
Another test I tried was, after I performed the "secure delete" and the file state changed to "unrecoverable", I ran the scan again, and they had returned to the "very poor" condition. Long story short, even after performing a "secure delete" several times on the same file(s), I was still able to recover them and open them with no problems and no loss of quality.
(Hmmmm...noticed a typo after I hit "submit" but couldn't find option to edit post title - even using "full editor".)