K date Luger how did they come up with a 'K'?

[Edward Tinker]

Gibson - page 106

these letter dates were the result of a gov't directed code intended to disguise the year of production as a means of circumventing the treaty of versailles. The letter designating a specific year was utilized by all manufactures.

Speed, Warren, et el
between 1930-34 nothing to show year made (paraphrase) ... however, the firm began using the prescribed letter codes.

I can not find Joop and Dons book to see what they said