Would this apply to pretty much all countries? Especially "testing is reserved for living patients"? A lot of countries are struggling to test enough living people.
Of course. If you're interested in detailed reporting, it gets fuzzy. False positives, false negatives, not testing, losing results.. Most stats aren't exact in many ways. This is NOT a US-specific phenomenon (healthcare is Excellent, when provided), and in some cases cause of death was NOT COVID-19 either, despite positive test. For deaths, it is a bit better, since most countries do keep tally in that area, but actual testing may vary wildly post mortem.
For the "waiting for evidence"-crowd (inaction), this is bad news. There's just no time when action is required NOW.
However, by buying time, we can ironically "wait for the evidence"!
- No claims of intentional undercounting.
- Some undercounting likely because testing is reserved for living patients where test results could affect how that patient is treated.
- Some undercounting may be temporary because of lags in test-results / reporting / tallying.