I see. I hadn't known about those earlier tests. A major problem with the tests - in general - is that many of them are not appropriately conducted - with the swab in the right place for the right amount of time - and thus there are false negatives, which are nearly impossible to trace, unless one were to take the same test twice within a couple of days.

I should note that I took the text, which arrived by mail, and I returned 2 days later. There was no virus, but I can see how it would have been very easy for me to have taken the test incorrectly.