What I've suspected all along....

If the first cases observed in China were from December, they'd have been contracted in November. It's likely that other cases had been ignored, but some of the symptoms cluster in fairly unique ways, so it's not likely that there were all that many of them. So the jump would have happened in November, with limited circulation then. Perhaps it was circulating in October, but circulation would have been more limited.

December would have seen travelers from Wuhan going to industrial and education centers. That might be in the US, but Italy has a special industrial connection to China, esp. northern Italy. But there are connections to California, Germany, Britain, other places. So I'm not surprised that there was some spread in December, perhaps very late in November (or possibly earlier, but the OP doesn't push quite that far). Asymptomatic patients make it hard to track, and it was masked in large part by flu. It may be offensive to say it, but most cases of COVID are very flu-like to the casual observer.

It does mean that by the time the announcement was made by WHO it was being transmitted in a few countries. Which means the horses were out of the barn before anybody realized that there had been horses in it.

This makes whatever time Chinese authorities spent covering up things even more valuable. It also means that without widespread testing weeks before the Germans came up with their first test containment had largely already failed. All the arguing, all the WHO announcements that were wrong before they'd been changed to be always right, all the "let's contain this" crap was treading water and arguing over who forgot to blow up the life rafts while the sharks circled.

I still think that the PRC was forced to its measures to stop something that was spreading fairly quickly and surreptitiously, and their measures failed. S. Korea succeeded because it spread in a fairly close community and they could test everybody in that community, and treat them in a fairly harsh fashion. Taiwan succeeded because it started off with better knowledge than the rest of the world had, and, like S. Korea, had a proper assumption that the PRC was not being forthcoming and honest, and had access to information that made tracking every person who could be infected easy, quick, and simple--just cross-reference some databases and send people out to check contacts.

possible, don't focus on the possibility that China early on also had no idea what it was dealing with and Mayr didn't want to seem alarmist. I think that Chinese leadership clearly has an openess issue, don't get me wrong there, but a lot of what WE are dealing with is attributable to us having an exceptionally poor president. We had more than two months of warning before the first case was diagnosed on our shore, experts were warning Trump to set up stout defenses and he did not, because of a belief that would hurt his chances at reelection.

It seemed to break out all over pretty much the same time.

came back with a mega-killing vengeance after mutating to a deadlier strain before the second wave.

The thing that causes me some concern is the SAR-COV-2 may be mutating toward a deadlier strain. China either completely missed or simply didn't detect some things that are happening now, like patients seeming to get better, leaving the hospital, only to crash out suddenly and die, or the thing that has been noticed in NYC, Boston and some other US cities where children are displaying a strange illness that seems to be covid19 related.

One of my concerns is the virus may mutate in kids, and then jump back to their parents with a killing frenzy. The 1918 virus mutated in the war trenches of WWII Europe and in the crowded civilian shelters of that war, and when it came back, it laid a decent amount of waste on the world.

this virus/epidemic which has been presenting with so many confusing variations. Thanks, Yo.