The same twitter thread (again, same person: director of UCL UGI) shows a Lancet article placing the first documented hospitalization on December 1, and a different source documenting a case in China in mid-November:
https://www.scmp.com/news/china/society/article/3074991/coro...
So yes, there are multiple lines of evidence. This isn't even remotely controversial. You're arguing that the sky is red, and your only counter-argument to the evidence otherwise is incredulity.
> are there any actual sequenced, dated samples from Italy in December? That's the standard of evidence here, not some crappy antigen test or unsequenced amplification hit.
I mean, you're inventing "standards of evidence" here, but as long as you're asking: yes. Dated, PCR-confirmed wastewater samples in Italy were purified by gel electrophoresis and sequenced.
https://twitter.com/BallouxFrancois/status/13280584020529684...
https://www.medrxiv.org/content/10.1101/2020.06.25.20140061v...