User blog comment:Zwann/Vasto Lordes in the Espada, let's analyze./@comment-1659217-20091118013728

Aizen only recruded those who 1. made a pact with him - Barragan, Starrk, Ulaquirra. Niell, 2. those that he could control/intimiate. Grimjow, Yammi, Nroitra (I think he gained some of her riestsu after attacting her and thus got to nr. 5 from 8), 3. Aizen did NOT know of Ulaqiurra 2nd release. 4. Aizen took the 3 strongest (in his estimation) with him and was very fustrated that they were not strong enough = the four strongest were Vasto Lordes or quite close - Niell and Tia too - Wonderwiss must also be. Ulaquirra was already a natural Arrancar; Barragan, Starrk, Tia and Grimjow all had fraction that were Adjudhas. Grimjow and his fraction were the first to be made arrancar by Aizan. If they found stronger Vasto Lordes in HM those hollows did not fill Aizen´s recurements: being controlable or willing to make a pact with him.