I’m out of the US right now and I had to present my passport (or passport number) three times before I could board: once while checking in online^, a scan when

I’m out of the US right now and I had to present my passport (or passport number) three times before I could board: once while checking in online^, a scan when dropping my bag, and then a third time in person when boarding the aircraft. ^ (and I’m pretty sure entering my number at checkin is the critical one that’s matched against any important lists, right?)