The two lineages were both present in some of the first infections at the Market in early December 2019 and in environmental samples taken at the market in mid December.
They couldn't have circulated for “a few months” because in that time, literally tens of thousands of cases would have been reported.
So you’d have to have a two SNP mutation from one of the first infected people in the world that would go on to infect basically everyone else in the world since Lineage B was reported first but soon died out. It’s not impossible (nothing really is) but would be extremely unlikely.
They couldn't have circulated for “a few months” because in that time, literally tens of thousands of cases would have been reported.
So you’d have to have a two SNP mutation from one of the first infected people in the world that would go on to infect basically everyone else in the world since Lineage B was reported first but soon died out. It’s not impossible (nothing really is) but would be extremely unlikely.