Despite the heavy smoke, I went out on Saturday for another virus test, this one dictated by an upcoming medical procedure and hence given not by the county but by my medical provider. Don't worry; I got the results today and it's still negative.
The testing center was set up in a parking lot of one of the provider's hospitals. I had an appointment time, but when I got there a few minutes early there were cars lines up in a row which turned out to be half an hour long. A screener read your ID through your closed window, and when I got to the tester, who wore shield as well as mask, she asked if I'd had this done before.
In addition to swabbing the lower nostril, there was a dab towards the back of the throat, which I hadn't had before and which was only briefly gagging. The tester said they don't go into the upper nostril any more, which leads me to expect that what I'd read about upper nostril and never experienced is merely a variation that further research on the virus led to be considered unnecessary by the time I had my first test.
Now I need to isolate until the actual procedure, which shouldn't be too difficult.