What Is The King Of Key Dates?

Hypothetical example:

A coin worth 5 wotzits was minted between 1908 and 1925. Here are the mintages
of it for each year. The size and shape of the coin each year was the same. There was one mint and the ruler and metal remained the same.

1908 - 4 million
1909 - 3.5 million
1910 - 250,000
1911 - 17 million
1912 - 98 million
1913 - 4,250
1914 - 12 million
1915 - 8 million
1916 - 154 million
1917 - 980,000
1920 - 4 million
1921 - 32 million
1923 - 75 million
1924 - 2 known
1925 - 198 million

In that list its obvious you have some very common years and some not so common

The key date there is clearly 1913
The semi keys are 1910 and to a lesser degree 1917
1908, 09 and 1920 would be scarce dates, but not keys in any sense

1924 is not a key date as its obvious it was probably an essay or a pattern
and with only 2 available - its unilkely you can ever buy one, unless you rob a
bank or the mint sells it to you. On the other hand, a 1913 coin you could buy
quite easily for the right amount of cash.