They can't say "refund" for the reason in my post immediately above yours. It's not a refund. A refund would be returning to the buyer what they gave for the product - cash (because you can't buy the expansion with cartel coins).
They should have actually said refund instead of appreciation. I believe most (not all) would have understood that but using the word appreciation gives a bad impression that one set of subscribers is more valued than the other. They should have worded it where it was clear it was a refund and not clouded it with the word appreciation. They need to learn how to use words correctly.
It's not a refund. It's an in-store credit, subject to all the limitations of an in-store credit.
Personally, if I had purchased the expansion within 30 days of the "free" date, I would demand the refund. I have no desire for any more cartel coins.