If you are talking about events they either use random.org or they have rules that tell you how they get the cards.
What mihall is saying, basically.
New releases do not go free to anyone
New Releases are obtained from buying NB packs (New Blood pack). This week the new releases were Plunk Raven Luke and Moegura. There is no preference in obtaining these cards, e.g a 5 level Novice has the same chance of getting a Raven in the NB pack as a 100 level Legend.