In most parts of the world, we have absolutely no idea how far the infection spread from about the end of October to at least February, so we can’t conclusively

In most parts of the world, we have absolutely no idea how far the infection spread from about the end of October to at least February, so we can’t conclusively rule out that kind of error until we can test lots of people for antibodies (this is the only way to confirm a case in a person who has already recovered). It would require the infection to be very contagious, and it probably would require us to have been pretty unlucky with the timing, but as far as I know none of that is contradicted by the available evidence.