Brain-Teaser 188: Family birthdays

From The Sunday Times, 29th November 1964 [link]

I wrote to an American friend on the 3rd February 1964, and told him of the coincidence of our family birthdays. My wife and I, our three sons, and our four grandsons all have our birthdays on the same day of the week every year, though all our birthdays are different. When I wrote, I used the usual English form of the date — 3/2/64 — and I gave all our birthdays in that form also.

My third son received a cable from my friend on his birthday in 1964, but later I was surprised to get a cable from him myself on my eldest son’s birthday. Next my eldest grandson received a cable on his right birthday, and I realised that we were all going to receive cables, but that my friend was, quite reasonably, reading the dates in the American form, i.e. he assumed that the letter had been sent on 2nd March 1964.

However, I did not write to put him right, and my wife was the next person to get a cable; this was not on her birthday.

What was the day and date of her birthday in 1964?

This puzzle was included in the book Sunday Times Brain Teasers (1974, edited by Ronald Postill).