Question about possible "Jusqu'a" rates in Canada 1931


Hello again,
You may notice that Chris Hargreaves's June 2013 APJ article features a cover from Edmonton to South Africa. The sender used 10 cents for postage and got whacked for postage due.
Some of you may know that with the help of my friends in the Canadian Aerophilately Society I collected Canada airmail rates that hopefully will be used in the next AAMS Canada and Newfoundland catalog.
Chris correctly notes that the rate at that time was 15 cents that covered airmail wherever it existed and surface otherwise.In this case the cover may have been carried to New York by air and then surface to London. Since there was not airmail to South Africa it probably went to South Africa by sea. If there was any air service inside South Africa it might have been carried there.
Hal Vogle suggested that perhaps the sender really wanted exactly what he typed on the cover "Airmail to New York City" and surface thereafter and he expected to get that service for 10 cents. We don't think there was a rate for that. I have to suppose the guy just guessed at the rate.
Do any of us know of  "up to" or "Jusqu'a" rates used in Canada at this time???
David Crotty