No, it was an AC flight number for an AC operated flight on a 014 ticket issued by Aeroplan.
There was no United on the ticket at all.
The YYZ MLL agent added it before we boarded YYZ-LAX.
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On another somewhat related matter, this is the SECOND time I've had this happen in the past year, and while I don't recall exactly how many times I've done a SDC on an Aeroplan ticket, I suspect it's at most 3, but maybe as high as 5. So still really bad.
I called right after midnight to do a SDC. My original OLCI boarding pass showed a ticket number and S100K. The concierge said she had checked me in, so I went to bed.
This morning, I tried OLCI again, and it failed right away. Meh.
At the airport, the agent prints my boarding pass and my bag tag, and what do I notice? COUPON REQUIRED. She felt really bad, because she'd circled/ticked various parts of the BP, including where the ticket number should have been
So she fixed that, printed a new one, and then I noticed neither boarding pass showed S100K. She thought nothing of it, because I was in the US priority check-in line (there was no one manning the counter to open the SE line, and there was only one person in the priority line, so I just used it), and J entitles me to priority. And I almost missed it because of the priority tag.
So she adds my Aeroplan number (easily, and it worked), and reprints the boarding pass and the bag tag.
She commented how I was really on my game. And she said "I'll never forget you, Mr. cow!" as I walked away
But that's a really annoying problem with same day changes on Aeroplan tickets that I keep running into. I lose my ticket number, and I lose my status (when in J, that's only good for concierges monitoring things and getting rebooked if the flight is cancelled before the gate hoard overwhelms the agents, and meal priority).
The need to fix this SDC crap.
Also, I'm very tempted to just not say anything next time and let the GA handle it. Maybe if GAs start complaining more about agent-printed boarding passes showing COUPON REQUIRED, the agents who print boarding passes will pay more attention.
My record for "no one noticing" is an agent printing it, and me giving it to a concierge for lounge access, and even I didn't notice it until it was handed back. But seriously, this should be like TSA Pre✓. If it prints with no valid coupon, it should go BEEP BEEP BEEP.