True, I had forgotton all about these actually, having not encountered one since my Atari ST. If he suspects this then I suggest running FIXMBR from the recovery console.
This is a common mis-conception. It has never been possible to recover overwritten data by using just software and appears to be generally accepted as totally impossible on a modern drive.I think boot n nuke writes 0s to the entire drive but I have been told that there is software you can get that makes it possible to recover on any drive, but the more times it has had different sets of data in different areas the harder it is I think.
I always thought that the only way to make data completely unrecoverable was to physically destroy the HDD.
It is or course totally possible to recover deleted files that haven't been overwritten. And sometimes to find fragments of information in the system page file or other temp files.