Re: 7% overprovisioning and a data protection nightmare
No different to bad / reallocated sectors that spinning media now transparently re-allocate on-the-fly when there's a problem and barely bother to tell you about it via SMART reporting (it's a minor statistic published nowadays, doesn't even warrant a more detail SMART warning/error report).
There is no way to ensure that the data on a drive isn't still present (and, no, nobody has ever recovered "historical" data from a magnetic drive even with the most expensive hardware in the world - go research it - but that doesn't mean that you overwrote everything, as you worry about with SSD). It doesn't matter the technology.
Don't give away drives that had your personal data on if you're worried about this. Do what every sensible person in the world does - just destroy the drive. No problems, no issues, no time wasted waiting for a disk to write several times over its entire capacity (if it can even do that any more), and no worry about "what you might have forgot" in terms of reallocated sectors, low level formatting, on-board Flash cache, etc.
Burn the damn thing down to ash. Problem solved. No matter what the technology.