From the Catholic Encyclopedia:
Even when specifically approved by the pope, decrees of the Holy Office are not infallible. They call for a true assent, internal and sincere, but they do not impose an absolute assent, like the dogmatic definitions given by the pope as infallible teacher of the Faith.
I maintain that the Holy Office letter demands a true internal and sincere assent by good Catholics.
The HOL is subject to question, not of the ordinary and universal magisterium, and thus not free from error. And it isn't even a "decree," is it? It's a "letter" on its own terms.
I respectfully question its contention that an "implicit" desire to enter the Church is sufficient.
Identify that concept in the OUM, Lover of Truth, if you can, please.