Regarding that specific case, everything relevant for us at the moment is behind the link you give and one internet search away:
It's dated "March 26, 2020" and it starts with "Italian researchers are looking at whether a higher than usual number of cases..."
If they were looking then, during the following three months we would have heard that they have found something? I understand they still haven't.
However, other research was done since: during the last months no virus was sequenced more often than SARS-CoV-2. The genomic information in the virus slowly changes and it can be used to determine the point when the virus started infecting humans:
"The origin of the regression between sampling dates and ‘root-to-tip’
distances (Fig. S3) provides a cursory point estimate for the time to the
MRCA (tMRCA) around late 2019. Using TreeDater (Volz and Frost,
2017), we observe an estimated tMRCA, which corresponds to the start
of the COVID-19 epidemic, of 6 October 2019–11 December 2019 (95%
CIs) (Fig. S4). These dates for the start of the epidemic are in broad
agreement with previous estimates performed on smaller subsets of the
COVID-19 genomic data using various computational methods
(Table 1), though they should still be taken with some caution."
That is one of the many reasons why "March 2019" doesn't fit. Another one is that COVID-19 hits every infected community very hard due to its fast spread, and such development just couldn't be ignored in any country, and even in the whole world -- look how much happened during last few months, and what happens when people try to ignore its existence.
It is very probable that the virus reached Europe before the start of 2020, even if it wasn't detected then. But not "March 2019."
"French hospital which has retested old samples from pneumonia patients discovered that it treated a man who had COVID-19 as early as Dec. 27"
And there is also a claim that in France there was a later reevaluated CT scan of the lungs that looked as a "typique Covid" that was initially dated "16 Nov 2019", but I haven't seen any independent confirmation of that claim:
I'm not aware of any proof for anything before Dec. 27 and it's possible there is or will be some. But I don't expect any other months than December or, at earliest and more unique, November.
It's dated "March 26, 2020" and it starts with "Italian researchers are looking at whether a higher than usual number of cases..."
If they were looking then, during the following three months we would have heard that they have found something? I understand they still haven't.
However, other research was done since: during the last months no virus was sequenced more often than SARS-CoV-2. The genomic information in the virus slowly changes and it can be used to determine the point when the virus started infecting humans:
https://www.sciencedirect.com/science/article/pii/S156713482...
"The origin of the regression between sampling dates and ‘root-to-tip’ distances (Fig. S3) provides a cursory point estimate for the time to the MRCA (tMRCA) around late 2019. Using TreeDater (Volz and Frost, 2017), we observe an estimated tMRCA, which corresponds to the start of the COVID-19 epidemic, of 6 October 2019–11 December 2019 (95% CIs) (Fig. S4). These dates for the start of the epidemic are in broad agreement with previous estimates performed on smaller subsets of the COVID-19 genomic data using various computational methods (Table 1), though they should still be taken with some caution."
That is one of the many reasons why "March 2019" doesn't fit. Another one is that COVID-19 hits every infected community very hard due to its fast spread, and such development just couldn't be ignored in any country, and even in the whole world -- look how much happened during last few months, and what happens when people try to ignore its existence.
It is very probable that the virus reached Europe before the start of 2020, even if it wasn't detected then. But not "March 2019."
I am aware of this confirmed case:
https://www.reuters.com/article/us-health-coronavirus-france...
"French hospital which has retested old samples from pneumonia patients discovered that it treated a man who had COVID-19 as early as Dec. 27"
And there is also a claim that in France there was a later reevaluated CT scan of the lungs that looked as a "typique Covid" that was initially dated "16 Nov 2019", but I haven't seen any independent confirmation of that claim:
https://www.francebleu.fr/infos/sante-sciences/coronavirus-u...
I'm not aware of any proof for anything before Dec. 27 and it's possible there is or will be some. But I don't expect any other months than December or, at earliest and more unique, November.