It’s certainly impossible that every single person that believes they’ve have it in December is correct. We’ve seen the exponential numbers of confirmed cases and how few actually had it once the tests were rolled out back at the end of January and start of February.
In those first weeks, we wouldn’t have seen 2, 2, 3, 6, 9, 9 etc etc for a month. We’d have started off with hundreds and would now be on about 3x-5x the amount of confirmed cases than we actually have.
People get bad coughs and Flu every year and yet according to my Facebook newsfeed, I apparently know some tens of people that had it from November 2019 to January 2020, or are certainly sure they did.