Agree with Cedric, this is a good move to eliminate confusion that exists when another STAR carrier books one of their FF members onto a TANGO transborder flight, and then receives grief from the member who finds s/he no longer earns status miles for the segment(s). And as pointed out, on these routes where AC competes with US carriers, the TANGO fare has actually been set higher than the T+ so "lowest fare" gives a full points accumulation fare. This is part of an evolving process to deal with the anomolies of a low fare environment. But like everything AC does, when they try to simplify things, they only make them more confusing. In a quest to eliminate the vast number of fares, AC created more fare codes! Then continues to regroup them into seemingly logical categories, but then inserts a whole other regime that doesn't quite fit the neat categories they've just created to simplify things!

When is a TANGO fare not a TANGO fare? When it's a TANGO PLUS fare. And when is a LATITUDE PLUS fare not a LATITUDE PLUS fare? When its a CITY PASS fare. And when is a LATITUDE fare not a LATITUDE fare? When it's a SUN PASS fare. Or something like that...