Ok, I'm sequence number 1 on a fairly full 738, SFO to EWR this morning. I checked in about 20 minutes after it was possible to do so. (Upgrades are so unlikely on this route that I don't sit by my computer waiting for the bell on OLCI.)

I find it a bit odd that no one on this fairly full plane checked in ahead of me, in this 20 minute window. Is it possible that we don't quite understand this sequence number?