I had a star alliance journey booked on AC and EVA. Checked in on AC, took a short haul AC domestic flight, AC probably screwed up (how do I know? it's AC). then EVA from Canada to TPE and eventually to DPS. Luggage delayed 24 hours at destination. So I'd assume most significant carrier is EVA. I had to purchase sundry items in DPS because of the delay.
Yes, you deal with BR because the final carrier is always on the hook for mishandling. MSC has nothing to do with this.
As someone based in North America, where do I write EVA to submit a Montreal Convention claim? Whatever airport is closest? I cannot find a corporate mailing address in North America, just local airport mailing addresses. I am guessing they will COMAIL my claim to the correct office but that's a guess. Thank you for your guidance on this mystifying issue. As I cannot find any concrete answers anywhere on the internet or here (everybody seems to do mtl convention claims on single airline jounries) I'll just claim with both AC and EVA so I stay within the 21 day filing deadline.
I'd start with the general online feedback form. Attach copies of your receipts there. Just keep it simple and say you're claiming reimbursement for purchases made in good faith. There's no need to mention the Montreal Convention at this point.
AC has nothing to do with reimbursing your expenses, so I'm not sure why you're filing a claim with them. As mentioned, it's only the final carrier that's responsible for reimbursing the passenger, regardless of who caused the mishandling.
i'll just submit it to the nearest airport although LAX appears to be a corporate/office address. and the US DOT is useful for moving these things along.
The DOT isn't the one responsible for enforcing the Montreal Convention. If push came to shove you'd be taking BR to court, not the DOT.