If they are non-stop DL operated flights, the AF/KL websites will definitely sell them as DL marketed (you will see a DL flight number on option as shown below) BE fares in E class with all the restrictions of those fares (including no mileage earn). So if OP is looking at booking ATL-ATH non-stop DL flights, there is no advantage to booking them on AF/KL websites. In order to avoid the DL marketing and get AF/KL marketing, you need to book flights with a connection (can be either in US or EU). AF/KL do not have a separate booking class for their Light fares (they will book into one of their coach classes based on fare basis code) and will earn according to AF/KL charts.




Here is a return option with BOS connection. In this case, KL marketing codes are used on both DL flights and the flights will have a KL R booking class and flights will earn according to partner chart for that KL fare class. The 'B' in second to last character of fare basis code identifies it as a KL Light fare (DL also uses this position to desiginate fare cabin type with B used for DL BE fares).