It’s because there is only one single place in the genome that you really want to track: the furin cleavage site (FCS). I assumed the wrong reason for using double CGG.
It’s not to distinguish natural from lab-made viruses (although it does do that).
It’s so that you can have a test in the lab for whether the FCS you have inserted is working or not. It’s so that you can “check your work”.
The unique spelling with double CGG is the only one out of the 36 possible configurations of arginine (the “R” in the “PRRA” FCS insertion) that allows you to track whether the cleavage you are trying to engineer has happened.
Steven Quay explains this at the 59:00 mark of his interview with Julius KIllerby, which is well worth listening to in its entirety, as it explains the odds of a lab leak vs. natural evolution, based on undisputed facts.
Given that full transparency from Chinese authorities is unlikely, assessing the probabilities is the best we can do. Fortunately, that has been done with with impressive scientific rigour by DRASTIC member Dr. Steven Quay MD, PhD in his technically detailed 193-page Bayesian analysis of 26 known facts about the outbreak:
https://zenodo.org/record/4477081#.YNAFry0ZNE4
which he explains in layman’s terms in his interview with Julius Killerby (cited in my comment above).
The advantage of this approach is that it follows the scientific method: laying out clearly its premises and calculations so that they can be challenged and tested by experts in the field.
The evidence is so convincing that, along with his influential piece in the Wall Street Journal (co-authored by astrophysicist Richard Muller)
https://www.wsj.com/articles/the-science-suggests-a-wuhan-lab-leak-11622995184
his Bayesian analysis—made available to both the WHO and the Biden administration—likely represents ‘the writing on the wall’ for public decision-makers. It was the ‘nudge’ indicating that keeping the story low-key was no longer an option, given the amount of technical expertise weighing in on the subject in public discussion.
In my view, given the dramatic quality of the statistical evidence, the Biden administration now finds itself the dog that caught the car. The three-month time period for a report from the intelligence community is likely only a breather to assess how to handle the truth of the matter politically with China, and no longer an attempt to establish what is actually true.