The file that appears immediately below this posting lists all of the works of Lewis in chronological order and in the location where it was first published or delivered (if spoken) as far as I am able to determine. Corrections welcome. Added April 14, 2011.
A recent visit to the Harry Ransom Center brought me into contact with two new letters by C. S. Lewis, written in October of 1952 to a Miss Ross/Mrs. Young about her new novel, Time's Corner, whose title she borrowed from a quotation by the Green Lady in Lewis's Perelandra. Therefore, I updated one date and added another one. The longer of the two letters is 453 words long, so it's a fairly significant one. However, Lewis does not really say anything new. He is cordial and complimentary to this author, promising to read her book again.
When will another new letter surface? They seem to keep appearing in various places, which is one of the major accomplishments of the three volumes of Collected Letters.