I just received a new discount code, and I don't recall ever seeing a discussion about these terms:
For North America bookings
- Valid on new bookings for the following destinations: Canada and United States of America.
- Offer: One-time discount of up to 15% off on all cabin classes per direction on undiscounted Air Canada-published base fares only, which form part of the applicable air transportation charges, when booking on aircanada.com
For bookings outside of North America
- Valid on new bookings for the following destinations: all destinations except Canada and the United States of America.
- Offer: One-time discount of the greater value of:
- 15% off on all cabin classes; or
- Up to CAD$50 off all Economy and Premium Economy class per passenger; or
- Up to CAD$150 off all Business and Signature class per passenger
Within North America, it's definitely giving 15% off the base fare.
Intercontinental, it's giving 15% off an expensive J ticket, and it seems to be $50 off each direction in cheap Y, which is substantially more than 15%. Without the code, the base fare was $370, and with it, $270.
So if these terms are new and consistently applied, they make no difference to me, but it makes the codes actually useful for people buying cheap base fares.