Isn't it also the case that a flash block (almost) always fails during write? So if the SSD
can't handle it with bad block relocation, the filesystem will mark the block as bad and put
one's data elsewhere. Unless it's a really dumb filesystem that hammers on the one block that
can't be relocated (like FAT floppy disks did!)
It's far worse if a block is successfully written, and then goes bad later, as often happens
to hard disks when they start degrading mechanically.