Last weekend, my wife and I flew from Seattle to Toronto on a connecting flight. First leg was SEA-ATL on AS, and then on a separate itinerary, we flew ATL-YYZ on AC. We had 2 pieces of checked luggage, and I knew that Alaska and Air Canada had an interline agreement between them, so when we checked in at SEA, I asked to have our luggage forwarded directly to YYZ. The agent struggled mightily to be able to generate the appropriate bag tags for this. After a little while, she managed to generate one bag tag, but not a second one. After about 20 minutes, she finally asked for help from a supervisor, who was able to generate the second bag tag in short order. We visually confirmed that the tags indicated both ATL and YYZ on them.

At ATL, we arrived in terminal D. Our AC flight was departing from terminal F, and we were able to make our way there relatively quickly (without needing to leave the secured area). That's when things starting taking a turn for the worse. I had placed an AirTag in one of our checked bags, and using it, I was able to see that the bag was still in the terminal D area. It never budged from terminal D, even as we boarded our AC flight in terminal F. You can imagine the feeling of helplessness as your flight pulls away from the gate and begins taxiing for take-off, all the while seeing on your phone that you're getting farther and farther away from your luggage!

Upon arrival at YYZ, the AirTag was still showing our luggage at ATL Terminal D. After clearing immigration, we went to the luggage carousel, and sure enough, our bags were nowhere to be found. We filed a delayed/lost baggage form with Air Canada and headed to our destination in Toronto.

Over the course of the next 48 hours, it was a bit frustrating trying to get updates on the progress of getting our bags delivered to us. Even though my AirTag showed our luggage moving from Terminal D to Terminal F the next day, and then arriving at YYZ later that evening, Air Canada's baggage tracking site kept showing the status as simply "Tracing still continues". And I got similarly unhelpful responses calling up both Alaska and Air Canada central baggage service. Neither side seemed to be able to provide amy information regarding the status of our luggage, even after I hinted to them the likely vicinity of the bags given what my AirTag was telling me. Fortunately, our bags were eventually delivered to us about 48 hours after our original flight, but I didn't receive any updates about our bag status until only a few hours before they were delivered, after the bags had been picked up by the local delivery service company.

The one interesting response I got from an Alaska rep I talked to the same night after arriving at our Toronto destination was that our bags never got the necessary clearance to be released to Air Canada. However, the delayed/lost baggage form we filed with Air Canada at YYZ would serve as that clearance, so it should get released the next day.

Does anyone know if this explanation makes sense? What clearance was I missing? What should I have done at SEA to secure that clearance and ensure our bags followed us to YYZ? And more importantly, what do I need to do when checking it at YYZ to ensure something similar doesn't happen again on our return trip from Toronto to Seattle next week, which is basically just the same two separate itineraries in reverse (ie. YYZ-ATL on AC and then ATL-SEA on AS, on two separate itineraries)?