The famous letter was issued by the Holy Office in 1949. The letter rejected Fr. Feeney's view regarding the salvation of non-Catholics. As I understand it, Fr. Feeney said that only persons who are formally members of the Catholic Church have any possibility of attaining eternal salvation.
That 1949 letter can be found on the ETWN website: http://www.ewtn.com/library/curia/cdffeeny.htm
But, I was unable to find that letter on the Vatican web site, vatican.va
I wonder if that absence means that the authorities in the Vatican no longer want that letter used as an authoritative teaching document of the Church's magisterium.
As any web search will show, lots of Catholics give lots of attention to the Feeney letter, some supporting the Holy Office's condemnation of Fr. Feeney's view, and some supporting Fr. Feeney's views.
But since the letter is not on the Vatican web site, I wonder if that means that the whole matter is, to some extent, rendered null and void.
Of course, there are many other documents available on the Vatican web site that address the issue of the salvation of non-Catholics.
But perhaps these other documents express the Church's teaching in a way that is slightly from how the Holy Office's 1949 Feeney letter put it. Perhaps the current bishops in the Vatican are not happy with how the Holy Office's 1949 Feeney letter expressed the Church's teaching.
Just a thought.