Not every event has 2 coupon per account limit , check the respective event descriptions which you wanna buy . Each event credit has its own limits and nothing is monthly or lifetime here . You buy credit and redeem and that particular credit has an expiry date which you can see in descriptions of credit and you have time until that to use your credits after redeemption . Now for EDU Credit usually each month new event comes and when new event come you can stack more new event credit in your same aws account . Hope i made things clear to you know , thanks for your interest .