Originally Posted by KLouis

Several domestic flights are operated by OA (codeshares). Although OA is a 100% subsidiary of A3, flights these flights don't earn miles on non-M+B programs as the airline is not part of *A. In those cases the system only allows for the M+B member's number to be filled in in the booking. In contrast, when booking "straight" domestic flights (marketed and operated by A3, such as HER and SKG) the feature is not blocked. In other words, "island hopping" earns no *A miles!