User blog comment:Arbington/DLC Theories/@comment-3053284-20100917151912/@comment-3061137-20100921001614

Given that the first Human Specter was Shepard who saved the Citadel the standard for humans joining would be rather high, there is also the fact that it isn't discussed how many specter candidates are considered each year. It could be that Shepard is the only new specter for a few years.