Originally Posted by NickB
This is because GDS are not good at dealing with carrier-specific booking classes. They recognise C, D and J as business class or F, A and P as 1st class booking codes are these are widely used.
Yes, and this can be very misleading. I was once proposed a "First Class" ticket on an AF flight between France and Indian Ocean (Reunion Island). The booking engine mistook "A" booking code for "First" whereas it is used by AF for "discounted Alize" (Alize class is a kind of premium economy). There is actually no First on this route.