Found them!  I'd forgotten to check the Foreword of Speak,Memory (Vintage International, p.13/14)

 

"All dates are given in the New Style: we lagged twelve days hehind the rest of the civilized world in the nineteenth century, /and thirteen in the beginning of the twentieth. By the Old Style I was born on April 10, at daybreak, in the last year of the last century, and that was...April 22 in, say, Germany; but since all my birthdays were celebrated, with diminishing pomp, in the twentieth century, everybody, including myself, upon being shifted by revolution and expatriation from the Julian calendar to the Gregorian, used to add thirteen, instead of twelve days to the 10th of April.  The error is serious. What is to be done? I find "April 23" under "birth date" in my most recent passport, which is also the birth date of Shakespeare, my nephew Vladimir Sikorski, Shirley Temple and Hazel Brown (who, moreover, shares my passport).´

 

( As a reward I treated myself to a pair of "Ferrero Rocher" special hazel brown bonbons!) 

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