For overwritten files you have to get into a multi-million dollar lab such as Homeland/FBI has.
For stuff that is not overwritten and the usual tools don't work, we send it to drivesavers.com
Bob
Hello,
I have deleted files on an external Olympus LS_3 dictaphone and am trying to recover them.
I've used several tools like Pandora, Easeus or PC Inspector but the recovered files are only recent files.
My files were deleted more than 15 days ago.
Do you know a tool that recovers older files?
Question 2: what if the file has been overwritten?
Thank you for you help!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic