A few years back, we were flying back from TSA (Taipei) via HND to SFO. From TSA to HND, we were in Economy; while from HND to SFO, in Premium Economy. I was OWS with BA. When we checked in at TSA, we were polite and courteous. We didn’t ask for any upgrades. The agent gave us our boarding passes and off we went. I didn’t notice that our seat numbers from HND to SFO were changed until several hours later at the HND lounge. We were pleasantly surprised and happy with the upgrade.

I guess that you don’t need to ask for the upgrade, since Sapphires are low on the pecking order. If your flight is overbooked, and there is enough to go around, you’d be sure that JL would get you upgraded. You don’t want to come across as feeling entitled. Good luck!