We know that information can be retreived after it has been deleted. There are several tools for file "undeletion" (Recuva, FTK, some tools contained in Caine, etc.)
I have heard as well, that data can be recovered, even after it has been rewritten. For this exact reason, the DoD used to approve methods which included (DoD 5220.22-M) to 7 (DoD 5220.22-ECE) overwrite passes. This is still a low bar, considering there are algorithms which include 35 passes (Gurmann).
Why, though? What papers, articles, or use cases have been published that suggest successful data recovery after single or dual pass of overwritting data?
Which software, methods, or tools allow me to analyze a given HDD for "further layers" (?) of recovery or overwriting?
(I know there is a different approach and dynamic to SSD, so for the time being, let's not meddle into it)