[JohnFen]

> but how can you determine what the old value was, given that it's now a random value multiplied by a random value with yet another random value added on top?

It's an extremely difficult problem, and in the best case you won't get a complete copy of old data. That's why this isn't an avenue of attack that you're likely to ever encounter.

This is the sort of thing that would only be considered by very wealthy attackers (governments and corporations), and even then only if they're very certain that the drive contains data of unusually high value.

But it is possible, and has been done, to extract useful data that has been overwritten a single time with zeros.

[Gordonjcp]

Yeah, no, it has not.

It's not possible, because there's no way to distinguish what the previous value was.