Combines molecular-clock inference on early genomes with epidemiological (birth-death skyline) simulation to estimate when the lineage that actually founded the epidemic achieved sustained human-to-human transmission, rather than just the tMRCA of sampled genomes. Concludes the successful transmission chain most likely began between mid-October and mid-November 2019 in Hubei, predating the December Huanan-market-linked cluster by weeks, and that over two-thirds of comparable spillovers in their simulations went extinct before taking off — i.e. plausibly several silent, unsuccessful spillovers preceded the one that became the pandemic. Companion argument to Pekar et al. 2022 (S-1): this paper supplies the timing side of the two-introduction case, the other supplies the topology/count side.
relevance_note: sets the earliest-plausible index-case date the whole timeline argument (and any lab-related-incident date) has to be compared against.