A case in point is perhaps the most famous conversion in 20th century English-speaking Christianity, that of C. S. Lewis. Not only is there some doubt among his biographers as to the exact date of the conversion, there seems to be some vagueness in Lewis's own writings on the subject.
Readers of Lewis will recall that his conversion took place in two stages. The first was his conversion from a pantheistic Absolute Idealism to Theism. This process is described in some detail in his memoir Surprised by Joy (1955), but the date is not given, beyond "the Trinity Term of 1929." The Trinity Term lasts, I gather, from about mid-April to about mid-June. It is therefore only a slight inaccuracy when Humphrey Carpenter in his book The Inklings refers to CSL's conversion in "the summer of 1929."
Unfortunately, there is no reference in any of Lewis's letters of 1929 to this event. The editor of the Collected Letters, Walter Hooper, guesses that the night when Lewis knelt down in his rooms at Magdalen and admitted "that God was God" was sometime in May 1929. But CSL does not refer to any spiritual change in himself until Jan. 1930 in a letter to Arthur Greeves, in which he refers to his renewed efforts to live a moral life and his afternoon "meditations" — but his language still implies a pantheistic, not a theistic, understanding of God.
And, in a letter that is assigned by the editor to Feb. 1930, Lewis writes to Owen Barfield that "the Spirit ... is showing an alarming tendency to become much more personal and is taking the offensive and behaving just like God." Hooper rightly notes that this experience is also described in Surprised by Joy ch. 14: "Idealism ... cannot be lived. It became patently absurd to go on thinking of 'Spirit' as either ignorant of, or passive to, my approaches." But this realization, as Lewis describes it in the memoir, came before the Trinity Term of 1929. This is impossible. The 1929 date must be incorrect.
Lewis also tells us in SBJ that "as soon as I became a Theist I started attending my parish church on Sundays and my college chapel on weekdays." It is not until Oct. 1930 that Lewis writes to Greeves that "I have started going to morning Chapel at 8." Although one cannot be sure when this habit began, it's unlikely that a man who had been going to chapel for over a year would write in this way.
I've therefore become convinced that Lewis misremembered the date of his conversion to Theism, and that it was very likely the Trinity Term (or even later) of 1930, not 1929, that saw the crucial change from Pantheism to Theism.
But is it conceivable that Lewis himself could have gotten this date wrong? He was notoriously vague about dates. We find him writing in July 1939 to a correspondent that "though I'm 40 years old as a man I'm only about 12 as a Christian." "About 12" would place his conversion to Christianity (which came in 1931) around 1927, which is too early on any reckoning. In Feb. 1946 he tells another correspondent that "my beliefs continued to be agnostic, with fluctuation towards pantheism ... till I was about 29." "About 29" would be in the year 1927 or 1928 (Lewis was born Nov. 29, 1898); again too early, on the evidence of the letters. Lewis's own recollection was too vague to be relied upon.
Oddly enough, we are in better shape concerning the second stage of his conversion, when he accepted Christianity. I say "oddly" because Lewis admits in SBJ that he himself remembered little about it. His letters from the time, however, fill in the blanks of the memoir. On Sept. 19, 1931, Lewis had a long discussion with J. R. R. Tolkien and H. V. Dyson in which his last objections to Christianity were overcome; the details are given in several letters to Greeves.
On Oct. 1, 1931, Lewis tells Greeves "I have just passed on from believing in God to definitely believing in Christ — in Christianity.... My long night talk with Dyson and Tolkien had a good deal to do with it." The conversation is not described in SBJ, and he does not mention in this letter the trip to the zoo he describes in SBJ:
I know very well when ... the final step was taken. I was driven to Whipsnade one sunny morning. When we set out I did not believe that Jesus Christ is the Son of God, and when we reached the zoo I did.There seems to be no documentation of exactly what day this was. Hooper states that it was Sept. 28, 1931, while George Sayer in his biography of Lewis says that it was Sept. 22. All we know for certain is that it had to take place between Sept. 19 (the date of the Tolkien-Dyson conversation) and Oct. 1 (the date of the letter to Greeves).
Well, what is the upshot of all this? Simply that Lewis's (and our) uncertainty surrounding the exact dates of his conversion(s) are not, in the final analysis, all that important. As he himself said: "As for what we commonly call Will, and what we commonly call Emotion, I fancy these usually talk too loud, protest too much, to be quite believed, and we have a secret suspicion that the great passion or the iron resolution is partly a put-up job." It is not Lewis's (or our) remembered decisions or emotions that finally tell the story of conversion; the true story, the important details, of all our biographies, can only be told from the perspective of Heaven. We are all unreliable narrators; but — "there is One Who is reliable."