From the OP, it appears that scientists knew exactly where to insert a furin cleavage site:
>“Since 1992 the virology community has known that the one sure way to make a virus deadlier is to give it a furin cleavage site at the S1/S2 junction in the laboratory,” writes Steven Quay, a biotech entrepreneur interested in the origins of SARS2.
That's such a mischaracterisation, I don't even know where to start. That Quay-guy obviously searched for "furin" on pubmed, found some papers (that don't even say that - and most definitely not for any coronaviruses) and thought it fit his thesis. If only viruses and infections were that simple!
> “At least 11 gain-of-function experiments, adding a furin site to make a virus more infective, are published in the open literature, including [by] Dr. Zhengli Shi, head of coronavirus research at the Wuhan Institute of Virology.”
The problem is knowing how to put in the furin cleavage site, and generally if it's done in the lab it's done by copying a particular sequence from an existing virus as scientists can't predict how to do it themselves (without copying) with current state of knowledge.
>“Since 1992 the virology community has known that the one sure way to make a virus deadlier is to give it a furin cleavage site at the S1/S2 junction in the laboratory,” writes Steven Quay, a biotech entrepreneur interested in the origins of SARS2.