I was denied entry into the LGA AC flying YUL-LGA-DFW-LHR, all on a single PNR and departing the same day (DFW-LHR was on BA). The agent tried scanning all 3 boarding passes and I showed my AS OWE card, but she insisted the computer said I needed AS Lounge+. I should have had access at connection points, based on the longhaul same-day BA flight, right? FWIW, I had no problem accessing DFW FL despite being a bit under 21.
Also, does this mean Canadian flights no longer grant access for elites? I was under the impression from earlier posts in this thread that international flights include access but the boarding pass scan said no.