If there was 800GB of static data, it was almost full, so the wear-leveling process wouldn’t be optimal and it would write over a small part of the flash cells over and over. In that case you could exceed the program-erase lifetime, but not necessarily the TBW. We know the total TBW was high, though, so it was even more excessive.

From what I’ve read, Apple has fixed this problem in a recent Mac OS version. Apparently, it was a swapping bug.