An important aspect is that dual fares is not the same as having different fare code and fare class. For instance:



So this is a Z fare, booked in J class. Not sure if that S at position 2 equals the dual fare feature or if it indicates direction - as S is a PE fare, and the primary fare is a business one. Would they somehow connect business and PE availability this way? Meaning that if S is unavailable in PE I would not be able to rebook this fare in Business?

Interesting link, thanks!