known_biases - Shared SARS-CoV-2 reference-genome / early-outbreak GISAID sequence collection reused across molecular-origin analyses. Sampling is biased toward early Wuhan cases actually sequenced and deposited (ascertainment/geographic bias); any systematic gap (missing early lineages, deposition timing) moves every clock/lineage/restriction-site analysis resting on it together, so findings built on it are correlated, not independent.