Some variants didn't show up in tests well. And being asymptomatic was/is really common. Why would you check if you don't have symptoms?

You can. But that still doesn't tell you if you've had COVID. Antibodies wane overtime and you can also test positive for antibodies after having had a vaccine. So even if you have been taking antibody tests every couple of weeks year now, you could have contracted it before the tests were available (it was about a year before they were publicly available in much of the US), or after a vaccination.