Here's the quote about the coded samples from the CDC:
[97.30]
Lo:
"They [the CDC] had a negative one [sample] and then send to us to test it.
And I see, for the CDC group of patients, most of them are negative in our hands, [indiscernible],
But the interesting part; and obviously we don't want to get into the too complicated thing;
And while they kick in [?], the so called negative control from a single patient, and repeated, I forgot, 15 times, 10 times, or something;
And that particular sample; we repeatedly identified as positive.
But that's a coded sample; you know, we did not know that that particular one is a, repeat, coded negative control,
and that one is positive."
It is difficult to understand all of Lo's speech in this section of the video, but it does suggest that there were other negative control samples that Lo consistently tested as negative, and that he consistently and repeatedly tested the one negative control as positive.