Here is a paper to back up your claims, where they apparently found traces of COVID-19 in Spain in March 2019. The paper is yet to be peer reviewed though:
It's an extraordinary claim but completely without evidence.
I've been following that, the only thing that is known is that there were some reactions activating tests, observed with the samples from March 2019, but not the whole virus, not even more markers, but just the two. Something like "a chemical probe that tests for presence of two times 10 letters", whereas a virus is something having 30000 letters. False positives using these kind of tests are possible, and even the "contamination" of the samples, and there isn't any demonstration that the authors made sure that wasn't a false positive.
Even worse, apparently nothing was actually isolated and preserved from the samples, in order to reproduce that, or isolate more letters, more a case of "the dog ate their homework" -- if I understood they claim they don't have the samples anymore?
In short: these researches used the search for 20 letters in the sample, which sometimes lies, even if that virus has 30000 letters, and they can't show that it wasn't a false positive. And even if the 20 letters have been there (only that month -- very improbable!), there's no sign that a whole virus has been.
The result from March 2019 is at the moment something that "needs more investigation" (if there is any material that can be tested again) but the presence of the virus during that month can't be established from that recently reported result.
Edit: the specification of the IP2 and IP4 gene tests that gave result in March 2019 sample:
Yeah, I've been thinking about how much false positives are with the result. I don't know about your background, but I am certainly not an epidemiologist, nor do I have the time to do the investigation, so I'd rather not get into the whole debate and wait for more published papers by people who are more knowledgeable than me in this area.
> I'd rather not get into the whole debate and wait for more published papers by people who are more knowledgeable than me in this area.
I've responded because it looked to me that you believe that the paper can "back up" the claims with, as you wrote: "traces of COVID-19 in Spain in March 2019."
I'm quite sure it can't show that COVID-19 was in Spain in March 2019, and even if the paper reports detecting IP2 and IP4 genes from the archived sample, even that is not certain.
No, I get it, I also find a lot of people who put links in to say "see, this is the definitive proof", I am not one of them; I've only put the paper into the response simply to add a bit more context to the other person's claim (since it was devoid of any form of links or reading material to back up his/her claim). I won't really believe that the study is true until there are more studies done on top of it and been peer reviewed (heck, peer reviewers can even be political!).
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.
Seems pretty inevitable that it would have spread.