The data recovered in this paper, though, was recovered by direct readout of flash chips in order to locate pages which had not actually been overwritten at all. This is a very different kind of problem and attack than the one that led to multiple-pass overwrites and falls into my point 3. The reason that multi-pass overwriting can be effective on SSDs is because the increased number of write operations encourages the SSD controller to remap more blocks in and out of the page space which increases physical coverage of the overwrite.
There is a potential benefit to multi-pass random write to SSDs in this case, but this paper shows exactly why you shouldn't do this: because the improvement in security from random overwrites is stochastic at best and cannot be guaranteed without full knowledge of the behavior of the controller, as can be seen in the paper in the drives which continued to contain remnant data after many passes.
As the paper finds, multi-pass overwrite is not a valid technique to sanitize SSDs, and is still cargo-cult security.
Yes like I already said multi-pass is not a good way to sanitize SSDs. However it does directly contradict your stance that data is irrecoverable after a full-write. It doesn't really matter that it's done via a direct flash chip readout. Literally anyone can do that. In comparison the cost of a SEM(which can't read out platters) approaches a million dollars.
There is a potential benefit to multi-pass random write to SSDs in this case, but this paper shows exactly why you shouldn't do this: because the improvement in security from random overwrites is stochastic at best and cannot be guaranteed without full knowledge of the behavior of the controller, as can be seen in the paper in the drives which continued to contain remnant data after many passes.
As the paper finds, multi-pass overwrite is not a valid technique to sanitize SSDs, and is still cargo-cult security.