That's my point, coverage (whatever your chosen metric) can only prove the absence of tests, not their presence e.g. if your coverage is 80%, then you know (10

That's my point, coverage (whatever your chosen metric) can only prove the absence of tests, not their presence e.g. if your coverage is 80%, then you know (100-80)% = 20% is definitely not tested since it never even ran in your tests. It doesn't tell you much about the 80%