In my wife's family, the tradition was to keep a penny or a larger set of coins for the year of a child's birth. This is something which we have continued with our kids and if a friend has a child, then they get an uncirculated mint set from me! OK, a bit off the subject, but if this was a widespread practice then it would account for a large number of survivals in high grade. I had a published theory about the survival of 1923 halfcrowns in high grade : it was the last year of high mintage of halfcrowns of the old type. (Low mintages in 1924-26.) My theory is that a (?large) bag of 1923 halfcrowns didn't get issued, and was belatedly released after 1928. By that time, the old designs were wearing rapidly due to shallow design. People getting uncirculated 1923s in their change might have thought "Hey, the old design! And in nice condition too!" and put one or two aside. And so more survived than other dates. Just a theory of course, but there has to be a reason why that date is so easy to find.