Given that coronavirus would not be observable until there is a cluster of symptomatic cases in a city (and a doctor with relevant experience who can observe multiple cases - here 李文亮), I find it highly unlikely that we could observe earlier cases, if they spread less rapidly or outside a city - or even within another city with less institutional knowledge.
> b) China would be highly incentivized to root out
Even if so, this doesn't form part of any prior. China being incentivized to act in that situation, doesn't affect how likely or unlikely that situation was.