Keep in mind that when flash memory is read, you don't get back 0 or 1. You get back (roughly) a floating point value -- so you might get back 0.1, or 0.8. There's extensive code in SSD controllers to reassemble/error correct/compensate for that, and LDPC-ish encoding schemes.

Modern controllers have a good idea how healthy the flash is. They will move data around to compensate for weakness. They're doing far more to detect and correct errors than a file system ever will, at least at the single-device level.

It's hard to get away from the basic question, though -- when is the data going to go "poof!" and disappear?

That is when your restore system will be tested.