If the aim was to make a genetically modified virus, why not start with SARS1 as the backbone? SARS1 is a well-characterized SARS coronavirus with known properties as a baseline, whose growth and purification in the lab are known.

I don’t make this point because I think COVID was not a lab-recombinant virus, I am simply making it because when this point was made to me, I did not have an answer.