Papal infallibility does not excuse the Pope from having what he's going to say examined by other people. First, the Pope is not infallible whenever he says anything, but only when he "speaks EX CATHEDRA, that is, when, in the exercise of his office as shepherd and teacher of all Christians, in virtue of his supreme apostolic authority, he defines a doctrine concerning faith or morals to be held by the whole Church" (from the definition of papal infallibility at the First Vatican Council). Second, one way that the Holy Spirit preserves him from error in such definitions could certainly by influencing him to have his words reviewed by others.
For example, Pope Bl. Pius IX, under whom the infallibility of the Pope was formally declared in 1870 as a doctrine of the Catholic Church, consulted with hundreds of bishops before defining in 1854 that the Blessed Virgin Mary was immaculately conceived. In the Bull Ineffabilis Deus declaring the dogma, he wrote: "We likewise inquired what the bishops themselves thought about defining this doctrine and what their wishes were in regard to making known with all possible solemnity our supreme judgment."
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