My only suspicion has been that the first name is historically accurate, and in this way he has always been sure of identifying the actual person, whereas every interloper would be misled by the family name.
Susmo bakarra dut, alegia izenak ez ote diren benetakoak, berak pertsona erreala beti identifikatu ahal izateko, eta edozein arrotz abizenen bidez nahasarazteko.