It would seem that the obvious conclusion from this excellent summary of the mystery of the origins of the FCS is that this novel FCS is the result of laboratory manipulation. I’m not sure why that point wasn’t made more strongly as the implications of this are far-reaching, to say the least. The relevant sections of your article that make this abundantly clear are the following:
“The researchers say the possibility of random insertion is too low to explain the origin of this motif. Surprisingly, the CGGCGG codons encoding the two arginines of the doublet in SARS-CoV-2 are not found in any of the furin sites in other viral proteins expressed by a wide range of viruses….For recombination to occur, there must be a donor, from another furin site and probably from another virus. In the absence of a known virus containing this arginine doublet encoded by the CGGCGG codons, the researchers discount the recombination theory as the mechanism underlying the emergence of PRRA in SARS-CoV-2.“