file not deleted

hello. windows 7, IE10, CCleaner v3.19.1721.

I run CCleaner and Drive Wiper to remove private files. Occasionally, I check the cleanup results with Piriform Recuva, which returns many unwanted, private files. It is baffling to me in three ways. First, some unwanted files were not overwritten. Second, Recuva is supposed to search for deleted files, but it finds files which were (I thought) not deleted, but simply resident in Temp Internet folder, etc. Third, some of the private files, found by Recuva, cannot be overwritten by Recuva. (Perhaps a topic for Recuva forum.)

What am I missing here?

I am grateful for any insight or assistance you can provide.

The latest Ccleaner build is v5.13.5460 so you are quite a bit out of date.

Latest build can be downloaded from here.

https://www.piriform.com/ccleaner/builds

some of the private files, found by Recuva, cannot be overwritten by Recuva.

If the files reside in the MFT it can't overwrite them, which is a similar description Recuva gives when that's the reason.