Baptism of Desire cannot possibly be visible.

The Council of Trent declares this:

CANON XVI -- If any one saith, that he will for certain, of an absolute and infallible certainty, have that great gift of perseverance unto the end, unless he have learned this by special revelation; let him be anathema.

If we cannot say with "absolute and infallible certainty" that we will go to Heaven, how could we possibly make such a claim about any non-Catholic, whether such an individual has been publicly baptized or not??? Clearly, BoD is not visible!

Of course, the Second Vatican Council reaffirmed the decrees of the Council of Trent in Lumen Gentium, 51.

Yes, if the Holy Office letter did, in fact, imply that, but clearly, as the Holy Office cited the Council of Trent, then it could not be implying that BoD was visible, for it would have contradicted Trent, and hence, itself for having cited Trent as an authority!

Well, "call him out" (if he is still alive, probably not), and unless he can name some of these "visible exceptions," then he ought to retract his statement.

He is dead but his writings are important for traditionalists. He never made the invisible-visible, explicit-implicit distinction.

Well, he should have!