I have come back from Cancun to Toronto, and on to Ottawa, on Feb 2. The Cancun to Toronto flight (handled by Mexicana check-in agents) has still not been credited to my Aeroplan account, although the Toronto to Ottawa flight that day, has credited to my account.

My Aeroplan number, and Star Alliance Gold status were printed on the boarding pass.

Should I assume that these miles will not be credited to my account (ie I will have to mail the ticket and boarding pass to Aeroplan to get the miles, for this flight), or is it still possible that the mileage will be credited to my account, without a need for me to do anything?

If the miles are not posted to my account, then what is the reason - ie what did the Mexicana agents do incorrectly to prevent such credit - and what should I ask nonAC Star Alliance agents (acting as check-in agents for AC flights) to do, to make sure this problem does not recur?

If the Mexicana flight was an AC codeshare flight with an AC flight number, I would try to use Aeroplan feature to request for a missing flight credit.

The flight was on AC coded on AC metal. The Aeroplan web site where one can email in the request for credit of missing miles, has a long list of exceptions as to the city of origin of the flight(ie numerous cities where AC check-in agents are not responsible for AC flights?), including Cancun.