It's because you're Canadian. It would be pretentious to use the phrase "evening doublet" on an invitation extended in the USA (or most of Canada, for that matter), but it might happen if the intention was to preclude anything but formal highland wear. The reference to a "dinner jacket"really isn't used much in the USA except, possibly, by pretentious people like me. But then I always note on the invitations I send out the ending time of the event with the phrase "carriages and chairs at 11 o'clock" or what ever time it may be that I want my guests to depart.