known_biases - Sampling began 1 Jan 2020, the day the market was closed and disinfection started, and animal-material collection only from 18 Jan after most live animals were removed — so an animal-negative result cannot exclude infected animals having been present, and any positivity pattern reflects post-closure residual environmental contamination. Collected/curated by a single actor (China CDC) with a 13-month raw-read release lag; everything resting on these swabs moves together if the sampling/curation was selective.