I had pretty bad Corona-like symptoms in late January/Feb in London. There was documented community transmission at that point, but it was very early (single digits) so it's technically possible but not mathematically likely that I had it.

The more I've mentioned this to people, the more I've heard people bring up their own stories and theories that they all had super bad flus this year unlike any other year and are all convinced they already had COVID. So everyone has convinced themselves that they already got it, no matter what city they were in at the time and whether they got sick in November or February.

This is hard to grapple with because I'm sure that any give year, a lot of people randomly get a bad flu like they've never had before with unique symptoms. And if you happen to be that person this year, then of course you would think you had this new disease that matches the symptoms. But given the lack of secondary community effects at the same time (other hospitalizations in your area), it's more likely that most of us are wrong and it's just a co-incidence. But if you are the person suffering the coincidence, it appears the same as if you are the person who actually got infected.

So who knows? I guess until antibody tests are widely available, none of us will know for sure.