In rec.antiques.radio+phono John Byrns wrote:
I wonder if the "K" might not have another meaning, such as a code to indicate
which of several factories the device was produced in? If that is the case, the
fact that "K" is the last letter in "week" might just be a coincidence.

I'm pretty sure it is a coincidence. I have only ever seen such indication
on some Philips equipment where the letters KW (kalenderweek,
kalenderwoche) are printed in front of a 3 or 4 digit code. Every single
other piece of equipment I ever saw with such a code only has letters with
another meaning in front of or after the date code.

--
Met vriendelijke groet,

Maarten Bakker.