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.

You're arguing a point that I never made. By all means, OP should keep it up!

Masks and procedures are effective but not 100%. I was religious about masking and distancing and hand washing and still got Covid Original Flavour(tm). Fortunately, I did quarantine after getting back from my travel (required: had to shut a house down) before even knowing I had Covid so my elderly relatives didn't get it from me.

Quarantining is very effective but is really inconvenient. You can't get every single person who wants to interact with you to quarantine for 14 days prior unless you are super important.