…Joseph Smith and Oliver Cowdery, according to their teaching, received the priesthood of Aaron in
1829. Given the circumstances of the Church in the United States in the 19th century and the means of social communication at that time, even though the new religious movement gained a considerable number of followers, the
knowledge that ecclesiastical authorities could have had of the doctrinal errors that were professed in this new group** was necessarily very limited** throughout the entire century.
…
In the 20th century, the Catholic Church
became more aware of the Trinitarian errors which the teaching proposed by Smith contained, though he used the traditional terms, and therefore** more and more doubts spread about the validity of the Baptism conferred by the Mormons**, in spite of the fact that the form, as far as the substance of the terminology goes, coincided with that used by the Church.
ewtn.com/library/theology/mormbap1.htm
(emphasis added)