It's actually been hypothesised from the beginning that ancestors of Covid-19 passed back and forth between humans and animals several times before taking its current form. The idea being that an ancestor of the virus was first transferred to humans where it 'learned' how to adapt to the human body before transmitting back to an animal host and mutated to become more deadly to humans and then transferred back to humans. This is partly based on the idea that a successful virus wouldn't adapt to be more lethal to its host and that close cousins of Covid-19 have been found in several species of bats and other animals.
This actually makes China a much better candidate than Europe for the place where the most important step in its evolution occurred. China has much more vibrant trade in wild animals for clothing, consumption, and traditional medicine. China also happens to be the place where the first reports of widespread hospitalisations occurred.
I don't think it's possible that Covid-19 in its current form could have floated around with its current high level of transmissivity or even the lower level of transmissibility of the Chinese strain without being detected for more than a month.
As we've seen from America's second wave (bumpy first wave?) the virus replicates exponentially (even with some social distancing), so tens of thousands of people can be infected within two weeks. So we ought to see pretty strong signal in ICU admissions within about 5 weeks of an outbreak (allowing ramp up time, incubation period, and time for symptoms to progress). We'd also expect to see all-cause mortality rates of people over 65 to increase significantly within about 7 to 8 weeks of the outbreak occurring as the average time to mortality is about 18 days.
I fail to see how it'd be possible for the health system of any developed nation to miss all that, but a developing country that has a culture of secrecy and suppressing information from both its own people and central authorities? Yeah I could believe that.
> Sort of like how we can find, retrospectively, intermittent cases of HIV back to the early part of the 20th century, but it suddenly exploded in the 1980s.
That's in large part because HIV collided with African urbanisation, significant international air travel deflation, an explosion of homosexual activity (unprotected sex), an industrialised blood transfer system, and a drug epidemic with administration using shared syringes. I can't think of a similar set of factors changing in our current society that could have allowed for the explosion of a coronavirus.