Unfortunately, not all cells/SSDs have the same lifecycle Some cell might fail after a few writes even.
If we could tell the amount of cells that are relocated vs. amount of extra storage cells that should tell enough?

OH's situation has me worried however I thought in such a situation the SSD would return a write error to the faulty location and continue working - I'm inclined to think that it's a controller logic issue (i.e. controller hardware, not the NAND part or firmware)