I think that should mean "NON DCS ORIGIN", DCS being the day-of-flight computer system AC uses for flights departing from RESIII-based stations.

Anything that happens in the RESIII world, AC can see and confirm in real time that you booked/checked-in/flew. For stations that don't use DCS/RESIII, that data may not be immediately available or available at all, requiring you to send in supporting documents.

There has been a push to bring more and more stations online with DCS/RESIII, for obvious reasons.

I know that SAN is a UA-handled station, and AC's data sharing with UA's system is kinda wonky. I had a few problems out of PDX last year, even though my FF number and status appeared on my UA BPs for my Jazz flights, the data having passed through from my PNR. Had terrible luck in points posting. I started asking the check-in rep to re-cycle my number through when I checked in and had much better luck. (FYI, I was posting to UA).