It wouldn’t surprise me one bit if they simply refunded all tickets and cancelled the promo: “Due to fraud (mass creation of accounts), we are unable to honor the promotion. As compensation everyone will get 500 Avios and if you book again next weekend, for every ticket worth 200$ or more, you will get 900 Avios instead.” ;-)
Would be an easy way out for them to blaim it on the customers. That way they wouldn’t have to deal with finding out which tickets were “legit” etc. either.