So it turns out I'll have meetings at NYC on both April and May.

For April, I can see that SEA-JFK and JFK-SEA has U spaces open around my dates, and EWR is not open for U, so I booked JFK both ways with GGUs.

For May, I can see that SEA-EWR has U spaces open around my dates, but SEA-JFK or either return doesn't have anything, so I booked SEA-EWR with gold upgrade fare (ran out of GGUs) and JFK-SEA back (not gonna hold my breath for upgrading on this).

Is there any general pattern on SEA-JFK/EWR routes? When booking April trip I thought people prefer SEA-EWR because of SEA-JFK is a red eye (even with upgrade, a non-lie-flat FC is not gonna help a lot in a red eye), that's why U is available on JFK routes. But then booking May trip denied my previous speculation (not gonna complain here).