Recently I've been seeing Z fares that AmEx IAP cannot beat and that don't show up when I call PTS to ask about IAP fares. (One of them was for a nonstop route with the expected IAP percentage discount on a much more expensive D fare, and I was looking at dates where both delta.dumb and EF were showing lots of Z class availability--and since it was nonstop, there would have been no married segment logic issue.) No one has been able to explain why they're not covered by the program. However, when I looked at the full fare rules for a couple of them, I found a line that says something like not being able to be further discounted. [Somewhat OT, but I've seen similar discounted Z or old FC G and A fares that show when I try to book through my employer's contract travel website link to delta.dumb, but give exactly a 0% discount. I'm not convinced that it's the explanation, but a DL supervisor once tried to tell me that these were already discounted fares, yet I know that our percentage discount varies with FULL Y getting the maximum percentage discount.] Maybe the IAP fares are like a corporate travel contract in how DL treats them.