Delta.com can be forced to bring up partner fares with tools like ITA Matrix Powertools browser extension. delta.com will generally not display any type of partner fares if you just use delta.com to do a flight search (it will usually just limit options to Delta fares). However, delta.com does not always pay attention to fares specified by ITA and will often present different fares on route than those specified (for example, if you want to upfare to a particular fare class using ITA, delta.com will often just ignore fare specified by ITA and just show cheapest available fares on a route instead). That seems to be true in this case as it ignores the KL Economy Light fares when specified by ITA and switches them to KL Main fares. In the case below when I tried, it switched from specified KL VL3J57B2 Economy Light fares to KL VL4J57M2 Main Cabin fares (as shown below). Priceline seems to be more reliable in preserving exact fares generated by ITA. Or, as you noted, you can just book these on AF/KL website.








One thing to be careful when booking on KL/AF websites is that they will often show DL coded flights/fares (instead of AF/KL ones) on non-stop DL metal flights to/from US. So you can actually end up with up with a DL E booking class on DL flights that earns nothing if you are not careful (AF/KL website only shows fare basis codes on flights, and not actual booking class, so it is important to see that you getting KL coded flights, and not DL coded ones when booking on AF/KL websites). In example below from klm.com, these are DL coded flights on DL BE fares and will have thus have DL E fare class and earn nothing.