Originally Posted by Syzygies
I just checked in for a flight tomorrow EWR to SFO, in the first minute, and I'm sequence number 28. My previous flight SFO to EWR, I waited 20 minutes and was sequence number 1.
Strange but possible. Either half the flight originates elsewhere in the east and already checked in, or the meaning of the sequence number has changed.
You're correct that others have checked in because of connecting flights.
When I flew HKG-EWR-IAH, I was easily Seq 1 for the EWR-IAH leg as I got to check-in to that flight 18 hours before those who just fly EWR-IAH could.
On the other hand, SFO is not a CO hub, so no one connects to your SFO-EWR flight.