These are absolutely a lower bound, especially with regards to the US.

My county public health administrations response to people showing symptoms isn't "come get tested", it's "stay home unless you're sick enough you think you need medical attention."

i.e. stay home, unless it's really bad.

One of the biggest hospital labs in the tri-county area only got supplies to perform testing about 5 days ago. And only enough for 3000 tests, with verbal agreements from vendors to make best efforts to continue supplies.

I am currently at home in the guest bedroom. I've had a cough, fever, headaches, etc since Friday. The clinic I called literally told me "stay home unless you're dying." So I may be one of those uncounted numbers (we had a fellow in the office from France, up through the 17th). Or I could just have inappropriately timed flu. But I don't think so. At least the symptoms have been super mild, so far, and don't seem to have been progressing.