hummm.....as far as I noticed, it is possible to buy a Flex+ fare for any day and then ask to change for your preferred day without price variation (flex+ = no Penalty). Nevertheless it is not guaranteed, not at all. One might end up with a ticket on EK to travel on a specific date with need to travel on another date, compatible or not with refund process time.....tricky. As the miles upgrades are tricky as almost never one can find reward seats on the routes were the miles are honestly earned. Lots of tricky things on skyward program, or at least on both major benefits of clocking miles in any airline: upgrades and guaranteed seats (lounge access and extra luggage comes with status not miles quantities). I truly believe the miles Stock was so great on client side, they invented this "spend your miles and reduce the cost of your ticket" to cover the fact that the miles have no value for a frequent traveler that find no practical use for them when really needs.