Or it was done once, and the "inoculation" byte came first. There were 4 buggy bytes. 3 would crash the card. 1 would fix the card ("inoculating" it). If they

Or it was done once, and the "inoculation" byte came first. There were 4 buggy bytes. 3 would crash the card. 1 would fix the card ("inoculating" it). If they only fuzzed once, or fuzzed with the same dataset (random.seed(1) // seed chosen at random), then they wouldn't catch it. Even then, it's pretty sloppy.