This series was created in Journal de Tintin in 1952. It was first published in books by Le Lombard in 1954. Jacques Martin was dissatisfied with the marketing policy of the company and went to Casterman.
Casterman began with the #3 of the series in 1965, Le Mystère Borg and relaunched #1, La Grande Menace in 1966. In 1974, Casterman published #4, Le Repaire du Loup and finally #2 in 1975. This explains why #2 has a publication year in Casterman which comes after #3 and #4.