Regarding the confusion with the codes, there are 2 types of codes. The gift codes, with content that was paid-for and the bonus codes, with content freely given by the staff.
Bonus codes have a limited validity, the expiration date info comes with the code. Gift codes are valid until redeemed, that is, they do not have an expiration date.
Quoting JuriJ's response to my enquiry:
Bonus codes have time limitation as they usually connect with some promo action, so we want them to be redeemed in a proper time. Gift codes as they are paid by users and supposed to be a gifts do not have any time validations.
Post edited December 31, 2012 by Densetsu