Originally Posted by goodeats21

I just experienced this so wanted to provide a data point.

Flew DAY->IAD->LHR->BKK. I went for my COVID test just under 72 hours from the departure of my first segment (DAY->IAD). I had an 8 hour layover in IAD.
When I got to the boarding gate at LHR for the Thai Airways flight to BKK, the gate agent immediately questioned my COVID test doc, stating it was not within 72 hours of the LHR->BKK departure. I took a deep breath, and calmly explained that the rule was 72 hours prior to the first departing flight, and handed him a copy of my flight itinerary. Went back and forth a bit, the started asking other Gate Agents for their thoughts, and then made a couple phone calls asking about it.

This was a tight connection, and boarding had mostly finished, so I was sweating a bit at this point. Eventually, he agreed that I met the requirements and let me on board.

I was worried about this, and actually had an appointment for a "backup" COVID test closer to my departure time, and within 72 hours of the departure of the BKK leg. I figured the results would likely come in while I was on the way to LHR, and could show them the email / report of that one. But United Airline makes you attest that you are not waiting for the results of a COVID test when checking in, so that prohibited that plan. Pretty sure they would not have found out about it, but I wasn't comfortable "lying" about it.

Everything turned out OK, and now waiting in hotel room for the arrival COVID test result.